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TOApproved for public release, distributionunlimited

FROMDistribution: Further dissemination onlyas directed by Commanding Officer,Frankford Arsenal, Philadelphia, PA; Aug1968 or higher DoD authority.

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d/A ltr, 3 Apr 1974

THIS PAGE IS UNCLASSIFIED

REPORT R.1896

SILENCERS

by

LEONARD W. SKOCHKOHARRY A. GREVERIS

AUGUST 19631

This document may be furthor distributed by any holder Onlyspecific prior approval of the Commanding Officer, Frankford Arsenal,Philadelphia, Pa. Attn: J8100.

DEPARTMENT OF THE ARMYFRANKFORD ARSENAL

"Philad.Iphia,.Pa. 19137

REPORT R-18036

SILENCERS

by

LEONARI W. SKOCHKOHARRY A. GREVERIS

AMCMS Code 554?2. 12. 46801.02

This document may be further distributed by any holder onlywith specifle prior approval of the Commanding Officer, FrankfordArsenal, Philadelphia. Pa. Attn: J8100.

Ammunition Development & Engineering LaboratoryFRANKFORD ARSENAL

Pl-iladelphia, Pa. 19137

August 1968

4d

DISCLAIMER NOTICE

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J.i

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Destroy this report when no longer needed. Do not return it to

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Iq

1:iABSTRACT

This report presents physical and functional descriptions andacouetical evaluation of various domestic and foreign silencere. andsilenced small arms weapons. Included are crods-sectional draw-ings and external view photographs 'if all systems tested. An acousti-cal evaluation oi each system is given in the form of far field soundpressure-time records. All major constituents of sound signaturesare identified and time-correlated with their sources in the system.Additionally, the report presents a record of silencing principlesand a theoret.cal analysis of the various noise generating phenom-enon.

i.i

TABLE OF CONTENTS

* Page No.

INTRODUCTION.................. . . .. .. ....

SILENCER PRINCIPLES. . .. . ............ 2

DESCRIPTION AND EVALUATIONS OF SILENCERS

TESTED. . ... o. . #*. .. .. .. .. .. ... .7

Caliber . 22 Hi-standard Pistol/F rench Silencer. 10

Caliber . 22 Silenced Hi-standard Pistol ..... 16

Caliber. ZZ Silenced AAI Experimental TestFixture . . .. . . . . . . . . . . .. . . . 23• ,

Caliber . 22 Hi-standard Pistol/FA Silencer . . . 31

Caliber . 30 M1903 Rifle/Maxim Silencer . . . . . 37

Caliber . 30 Silenced MI Carbine . . . . .. . 47 FCaliber . 32 Silenced Sleeve Gun .............. 5sCaliber . 32 Silenced Welrod Pistol. . . . .... 58

9 mm Silenced Welrod Pistol ............ ... 669 mm Silenced Sten Submachine Gun . . . . . . . 72

Silenced Sten Barrel, Type I ........ ... 76Silenced Ster. Barrel, Type . . . . . .. 82

9 mm P38 Walther Pistol/AAI Silencer. . . . .. 88

9 mm Walther MPK Submachine Gun/West GermanSilencer ....... ................... ... 94

Caliber . 45 Silenced M3 SubmachineGun . ................. 100

Bell Laboratories Silenced Barrel .... .. 100AMF Silenced Barrel .............. . I.. 1iz

CONCLUSIONS . ............ . . . . . . 119&

RECOMMEr'DATIONS. ................ 123

APPENDIX A - Ballistic Crack Field . . . . . . . . . 125

[9,,I.I

Page No.

APPENDIX B - Subsonic Projectile Flight Noise. . 128

APPENDIX C - Gun Muzzle Blast ......... ... 132

APPENDIX D - Gun Silencers ............. ... 145

APPENDIX E - Silencer Techniques & RepresentativePatents 4 .. .......... 158

APPENDIX F - Relative Loudness of Discreet SoundPulses ..... .............. .. 189

BIBLIOGRAPHY .............. .................. 193

LIST OF PATENTS ..... ................ . .. .98

DISTRIBUTION. . . . . . . . . . . . . . . . . . 206

List of Tables

Table

I. Caliber . 22 H'-standard Pistol/FrenchSilencer ....... ............... ... 13

II, Caliber . 22 Silenced Hi-standard Pistol . 22

III. Caliber . 22 Silenced AAI Experimental Test

Fixture ....... ............... ... 28

IV. Caliber . 22 Hi-standard Pistol/FASilencer ............. ................ 35

V. Caliber . 30 M1903 Rifle/Maxim Silencer . . 42

VI. Caliber . 30 Silenced ?Ml Carbine . .... ... 50

VII. Caliber . 32 Sienced Sleeve Gun ...... .. 57

Vill. Caliber . 32 Silenced Welrod Pistol . . .. 63

iv

ad

Ii

Table Page No.

IX. 9 mm Silenced Welrod Pistol ....... .. 69

X. 9 mm Silenced Sten Submachine Gun, TypeI Barrel ..... ................ .. 79

XI. 9 mm Silenced Sten Submachine Oun, TypeII Barrel ....... ................ ... 86

XII. 9 mm P38 Walther PistcIAAI Silencer. . . 91

XIII. 9 mm MPK Waltber Submachine Gun/WestGerman Silencer . ..... .......... 98

XIV. Caliber . 45 M3 Submachine Gun/Bell Labora-tories Silenced Barrel ............. ... 109

XV. Caliber . 45 M3 Su.abmachine Gun/AMF Si-lenced Barrel ..... .............. ... 117

XVI. Physical, Functional, and Acoustical Param-eters of Silenced and Unsilenced Small ArmsWeapons ....... ................ .. 121

List of Illustrations

Fig itre

1. Cross section. Caliber . 22 Hi-standard Pistol/French Silencer ...... ............ 11

2. Caliber . 22 Hi-standard Pistol/FrenchSilencer ............ .... ............ 12

3. Sound Pressure-Time History, five meters toside, Caliber . 22 Hi-standard Pistol (Unsi-lenced), Using Long Rifle Cartridge. . .. 14

4. Sound Pressure-Time History, five meters toside, Caliber . 22 Hi-standard Pistol (Unsi-lenced), Using Long Rifle Cartridge. . . . 15

'P

Figure Page No.

5. Sound Pressure-Time History, five metersto side, Caliber . 22 Hi-standard Pistol/French Silencer, Using Long RifleCartr'idge. ............. ............... 17

6. Sound Pressure-Time History, five metersto side, Caliber . 22 Hi-standard Pistol (Un-silenced), Using Short Cartridge (29-gr pro-jectile; velocity, 1050 fps; peak pressure,16000 psi) ..... ............... .. 18

7. Cross section, Caliber . 22 Silenced Hi-standard Pistol .... ............. ... 19

8. Caliber . 22 Silenced Hi-standard Pis.tol . . 20

9. Caliber . 22 Silenced Hi-standard Pistol,Disassembled ..... .............. ... 21

10. Sound Pressure-Time History, five metersto side, Caliber . 22 Silenced Hi-standardPistol, Using Long Rifle Cartridge . . . . 24

11. Cross section, Caliber . 22 Silenced AAIExperimental Test Fixture ........ ... 25

12. Caliber . 22 Silenced AAI ExperimentalTest Fixture ....... ............ .. 26

13. Caliber . 22 Silenced AAM Experimental TestFixture, Disassembled. .......... ... 27

14. Sound Pressure-Time History, five meters toside, Caliber . 22 Silenced AAI ExperimentalTest Fixture, Using Long Rifle Cartridge . 30

15. Cross section, Caliber . 22 Hi-standardPistol/FA Silencer ... .......... ... 32

16. Caliber . 22 Hi-standard Pistol/FA Silencer. 33

17. Caliber . 22 Hi. standard Pistol and FA Si-lencer (with Tape Removed), Disassembled. 34

vi

Figure Page No.

18. Sound Pressure-Time History, five metersto side, Caliber . 22 Hi-standard Pistol/

FA Silencer, Using Long Rifle Cartridge . 36

19. Cross Section, Caliber . 30 M1903 Rifle/Maxim Silencer .. ........... .. 38

20. Caliber . 30 M1903 Rifle/Maxim Silencer . 39

21. Maxim Silencer for Caliber . 30 M1903Rifle.' ... ............. . . 40

22. Maxim Silencer for Caliber . 30 M1903Rifle, Disassembled ... ...... .. 41

23. Sound Pressure-Time History, five metersto side, Caliber . 30 M1903 Rifle jUnsi-enced) Using Subsonic Cartridge. .... .. 44

24. Sound Pressure-Time History, five metersto side, Caliber . 30 M1903 frile/MaximSilencer, Using Subsonic Cartridge . . . 45

25. Sound Pressure-Time History, five metersto aide, Caliber . 30 M1903 Rifle/MaximSilencer, Using Subsonic Cartridge . . . 46

z6. Cross section, Caliber . 30 Silenced MICarbine ....... ............. ... 48,

27. Caliber . 30 Silenced MI Carbine .... ..... 49

28. Sound Pressure-Time History, five metersto aide, Caliber . 30 Silenced MI Carbine. 51

Z9. Cross section, Caliber . 32 Silenced SleeveGun ....... ................. ... 53

30. Caliber . 3. Silenced Sleeve Gun, side view. 54

31. Caliber . 32 Silenced Sleeve Gun, top view . 55

vii

Figure Page No.

32. Caliber . 32 Silenced Sleeve Gun, Dig-assembled ..... .............. .. 56

33. Sound Pressure-Time History, five metersto side, Caliber . 32 Silenced Sleeve GemwiLh Old Rubber Baffles .......... ... 59

34. Sound Pressure-Time History, five metersto side, Caliber . 32 Silenced Sleeve Gunwith New Rubber Bafilei.. ......... ... 60

35. Cross section, Caliber . .32 Silenced WelrodPistol ....... ................ .. 61

36. Caliber . 32 Silenced Welrod Pistol . . . . 62

37. Sound Pressure-Time History, live meters toside, Caliber . 32 Silenced Welrod Pistol 65

38. Cross section, 9 mm Silenced Welrod Pistol 67

39. 9 mm Silenced Welrod Pistol ..... ...... SC

40. Sound Pressure-Tine History, fivn meters toside, 9 mm Silenced Welrod Pistol (lessSilencer Section), Using Reduced ChargeRound . d................. ...... 70

41. Sound Pressure-Time History, five meters toside, 9 mm Silenced Wclrod Pistol with OldRubber Baffles, Using Reduced Char&;,Rotind ................. 71

42. Sound Pressure-Time History, five meters toside, 9 mm Silenced Welrod Pistol with 'NewRubber Baffles, Using RedIACed ChargeRound ......... ............... .. 73

43. Sound Pressure-Time History, five meters toside. 9 mm Silenced Welrod Pistol with NewRubber Baffles, Using Standard NATO Round(Projectile Muzzle Velocity, 930 fpd) . . . 74

viii

Sw

u Page No.

56. Cross section. 9 mm MPK Walther Subm%-chine Gun and West German Silencer . . . 95

57. 9 mm MPK Walther Submachiie Gun andWest Ger,-an Silencer ........ ..... 96

58. 9 mm MPK Walther Submachinc Gun/West German Silencer ............ ... 97

59. Sound Pressure-Time History. five metersto side. 9 mm MPK Walther Submac)'-eaeGun without Silencer. Using Subsonic car-tridge ....... ............... ... 99

60. Sound Pressure-Time History. five metersto side. Bolt Slap. 9 mm MPrt WaltherSubmachine Gun/West German Silencer.without Cartridge .............. . . .. 101

61. Sound Pressure-Time History, five metersto side, 9 mm MPK Walther SubmachineGun/West German Silencer, Using SubsonicCartridge ...... ............... . 102

6Z. Sound Y'ressure-Time History. five metersto side, 9 mm MPK Walther Si~bmachireGun/West German Silencer. Using Sub-sonic Cartridge and with Weapon and Si-lencer Wrapped with Attenuating Mate-rial ........... ................ .. 103

63. Caliber . 45 M! Submachine Gun .. ... . I.. 104

64. Cross section. Caliber . 45 Bell Labor-tories Silenced %f 3 Submachine GunBarrel ......... ............... .. 106

65. Caliber .45 13 Submachine Gun/Bell"Lboratories Silenced Barrel ...... .. 107

xul4

Figure Page No.

44. 9 mm Silenced Sten Submachine Gun,

Showing Type I and Cype II SilencedBarrels ..... ................ 75

45. Sound Pressure-Time History, five meters toside, 9 mm Silenced Sten Submachine GunBolt Slap, without Cartridge ....... 77

46. Cross section, 9 mir. Silenced Sten SubmachineGun Barrel (Typel) .) .......... 78

47. Assembly, 9 mm Silenced Sten Submachine GunBarrel (Type 1) in Test Fixture ......... 80

48. Disassembly, 9 rnm Silenced Sten S'.LbmachineGun Barrel (Type I) and Test Fixture. . . . 81

49. Sound Pressure-Time History, five meters toside, 9 rnm Silenced Sten Submachine GunBarrel (Type I) in Test Fixture. . ..... 83

so. Cross section. 9 mm Silenced Sten SubmachineGun Barrel (Type i). .... ........ 85

51. Sound Pressure-Time History, five meters toside, 9 mm Silenced Sten Submachine GunBarrel (Type 11) in Test Fixture ..... 87

52. Cross section, 9 rnm P58 Wat-ther Pistol/AAI Si!encer .... ....... . . ...... 89

53. 9 mm P38 Wa!ther r-stol/AAl Silencer. . . 90

54. Sound Pressure-Time History, ten meters toside, 9 mm P38 Walther Pistol without Si-lencer, Using Subsonic Cartridge ........ 92

55. Sound Pressure-Time flistory, ten metersto side, 9rmm P38 Walter PietoJ/AAM Si-lencer. Using Subsonic Cart: icge. ..... 93

ix

Figure Page No.

56, Cross section. 9 mm MPK Walther Svbma-chine Gun and West German Silencer . . 95

57. 9 mm MPK Walther St-bmachine Gun andWest German Silencer ........ ....... 96

58. 9 mm MPK Walther Submachine Gun/West German Silerncer ........... ... 97

59. Sound Pressure-Time History, five metersto side. 9 mm MPK Walther SubmachineGun without Silencer. Uaing Subsonic car-triige ..... ................. ... 99

60. Sound Pressure-Time History. five meterst- side, Bolt ": _. 9 mm MPK WaltherSubmachine GunrWeb, (-,erman Silencer.without Cartridge .... ............ . I.. 101

61. Sound Pressure-Time History, five metexrto side, 9 mm MPK Walther SubmachineGun/West German Silencer, Using SubsonicCartridge .......... ............... 102

62. Sound Pressure-Time History, five metersto side. 9 mm MPK Walther SubmachineGun/West German Silencer, Using Sub-sonic Cartridge and with Weapon and Si-lencer Wrapped with Attenuating Mate-rial ...... .................. . .. 103

63. Caliber .45 M3 Submachine Gun ....... 104

64, Cross section, Caliber .45 Bell Labor-torier. Silenced M3 Submachine GunBarrel ..... ................ .. 106

65. Caliber . 45 M3 Submachine Gur,/BellLaboratories Silenced Barrel .... ...... 107

x

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.lI

Figure Page No.

66, Disassembly, Caliber . 45 Bell Labora-tories Silenced M3 SubmachineGun Barrel. 108

67. Sound Pressure-Time History. ten metersto side, Caliber . 45 Submachine Gun

Barrel (Standard, 7. 5 inches long) in

Test Fiature ........... ............ 110

68. Sound Pressure-Time History, 4. 6 metersto side, C0Liber . 45 Be01 Laboratories Si-

lenced M3 Submachine Gun Barrel in TeatFixture .............. ............... 11

69. Cross Section, Caliber . 45 AMF SilencedM3 Submachine Gun Barrel .......... ... 113

70. Caliber . 45 M3 Suzbmnachine CunIAMF Si-lenced Barrei .......... ............. 114

71. _11.,sembly, Caliber . 45 AMF Silenced M3S..bm~chlne Gun Barrel and Tiet Fixture 115

"72. DMsassembly. Ca)iber . 45 AMF SilencedM.S Submachina Guz. Barrel and TestFixture ........ ................ . 116

73. Sourd Pressure-Time History, ten metersto side, Caliber .45 M3 Submachine GunBarrel (5. 6 in. long), without Silencer,in Test Fixture ..... ................ 118

74, Sound Pressure-Time History, five mnetersto side, Caliber . 45 AMF Silenced M3 Sub-

machine Gun Barrel in Test Fixture. . . . 170

xi

u=iczTOr P u AW.4Y MW

INTROD UCTION

"Throughout the history of firearms, gun noise has been of con-siderable concern to the military. Prior to firing, anti-:ipation of theear shattering affects tends to make the gunner flinch, resulting ina consequent deterioration of his aim. After firing, the gunner isusually in a state of temporary deafness. To the eneroy, Sun noisereveals presence vand. often, the location of the firer, thus invitingdefensive or offensive reaction. From the above alone it becomesevident that a "silent" weapon is to be iound indispenable in covertoperations.

Of the various noises associated with firi: . a conventionalsmall arms weapon, the most significant is the muxzle biast causedby escape of prcpellent gases after the projectile exits from thetarrel. Hunrdreds of patents, w.ar and police records, and otherliterature are witness to the efforts, for nearly a century, to elimi-aate small arms muzzlt blast. Notwithstanding time, eWtort, andinterest, no completely satisfaztory silenced weapon has yet beenproduced.

The lack of theoretical literature on silencing a firearm testifiesto the still inadequvte understanding of the principles of sound gener-a'jon anid Wtenuation in a small arms weapon, Perhaps the failure totheoretically define noise problems can be attributed to the virtual non-existenc:e of thorough and reliable experimental sound data f~ornexisdtng silenced and unsilenced weapons. This lack of experimentaldata is partia~ly due to only recent development of adequate soundmeasuring equipmentl 8 * and r artially due to the corrplexity of theproblem.

This report is intended to give an insight into the present stateof knowledge 3f silencing a smal arms weapon. Essentially, thecontents consist of physical, functional, and acoustical data on anarray of silenc;d weapons felt to be represenitat' re. The tound eval-uation presented here is cursory. primarily because of the complixityof the protlem. First, the gun muzzle noise is only one** of the manypossible noises teing generated by eLuch given system. Second, thesound of interest is directional and attenuates nonlinearly with distance.

*See Bibliography.**See, for exam-ple Appendices A and B

I

'OWN

Third, terrain and weather hav, a palramowit effect on the noise beingperceived in the far field. Fourth, the physiological response of alistener to a given sound is very strongly dependent on the backgroundnoioe and on his current psychologice! state. Many of th,• aboveproblems are too involved; others i.re beyond the scope of presenttheoretical knowledge. The rcsalts presented herein are only those feltto be esser,.ial and experimentaily reproduciblt.

All sound measurements presented were taken in the far fieidand direckly to the side of the weapon. This permitted application ofthe linearized acoustic theory and precented an undistorted 5equenceof acoustictl events. The sound signature of each weapon eescribedwas reco.-dec' in pressure-time coordinates sufihciently• expanded toshow each major constituent of the muzzle noise. Identification ofeach major !ound sourcp wvrs r.ccomplished through time-correlationof the sound scope trace with the various weapon functions occurringduring the firing cycle.

A bibligoraphy of books, reports, and patents pertinent to si-lencing a weapon 4s included for reference. 'Worx- pertaining moreto basic rcie'wes were included only when specific reference was madeto such works in preparation of this report. A few of the fragmentarytheoretical efforts, directly pertinent to silencing a weapon, are pre-sented as appendi,:es.

SILENCER PRINCIPLES

Muzdle noise of small arms weapons, silenced or unsilenced,occurs due to the following:

1. Air or propelleiat gis discharge preceding the projectile

exit. This consists primarily of the precursor wave pl-enomenonand tne propellent gas blow-by (and, of course, ;:eflections of thesetwo inside the system).

2. Projectile emergence and abrupt volumetric displacementof the air mass by the projectile at the weapon muzzle. This eifect,although insignificant in unsilenced weapons, requires atlentirit insilenced systems.

2

1

3. Air or propellenti gas discharge (or inflow) following pro-Jectile exit. This consists essentially of the initial uncorking ofinternal system pressure, the subsequent discharging jet turbulence,and the affects due to reflections of these inside the system.

The three noise sources are relatively independent of each other and,consequently, require different techniques for their attenuation. Thue,when designing or evaluating a silenced weapon it is usually necessaryto treat each noise source individually.

A projectile traveling ia a gun barrel accelerates and compressesthe air immediately atead of it. The precursor pressure wave thusgenerated is substantial in most weapons, even the ones with subsonicprojectile velocities. Prior to exit from the gun barrel, the precursorwave front generally consists of a shock which reaches a pressure ofseveral atmospheres. Upon exit from the gun. barrel, the precursorwave gives r'ise to a positive sound pulse in the far field. The sound Ipulse is generally of a sawtooth configuration, beginning with a shockand ending with an exponential pressure decay with time. In some si-lenced weapons this precursor sound pulse constitutes the dominantnoise source.

The abrupt exit of the projectile Itself generates a substantialnoise in some silenced weapons. This is especially common in weap-ons whose silencer exits are partially or completely restricted byflexible materials, such as sponge, rubber, felt. etc. In these casesthe exterior surfaces of deforming flexible material and the movingprojectile generate sound. To a certain extent the same phenomenon

also exists when the projectile emerges through a hole in a baffle.These effects can be expected to cccur even when the projectile isneither followed nor preceded by high gas or air pressures. Thesound signature in the far field lue to abrupt projectile emergencefrom the muzzle consists usuallyofanN-wave pulse. The magnitudeof this pulse depends primarily on the projectile velocity, diameter,and length, and on the silencer muzzle configuration, *

In an unsilenced subsonic weapon, the hot propellent gases dis-charging into the atmosphere after the projectile exit constitute thedominant source of muzzle noise. The initial sound pulse is generallysimilar in shape to the precursor pulse described above, but substantially

*This phenomenon is not to be confused with designations on scopetraces where "Projectile Exit" is meant to represent the generaltime of an event.

3

I o

greater in magnitude. In many unsilenced weapons this muzzleblast exceeds the limits of the firer's auditory safety and can be ofsufficient magnitude to stun him. In silenced weapons, the maj orportion of the propellent gas generally escapes into the atmosphereafter the projectile exists from the silencer. However, by this timethe gases have expanded to the total volume of the system and thegas pressure behind the exiting projectile is low with a correspondinglylow resulting sound pulse pressure. The sound pulse is again similarin shape to the precursor pulse; however, it may be further modified b-wave reflections within the silencer.

Blow-by it the leakage of propellent gases past the projectilewhile it is still inside the weapon. This condition occurs due to anysignificant clearance between the projectile and the gun barrel orsilencer. Since the accuracy of the weapon is generally impaired ifthe projectile touches any hard surface after leaving the gun barrel,most silenct . are designed with an adequate projectile clearance.!n some silenct.- this clearance is so large that a good portion of thepropellent gas escalpes prior to projectile exit, and blow-by represenp.sa significant sounc sowtrce In the system. The blow-by sound pulse -ogenerally a positive shock, followed by an exponential pressure decay.In come cases, when the projectile velocity is high, the blow-by canarrive at the silencer exit at almost the same time as the projectile.In this case the blow-bj sou.nd pulse will merge with, rather than pre-cede, the main gas discharge sound pulse.

Theoretically, a gas or air jet discharging into the atmosphereat a steady rate should not generate any significant noise. However,due to turbulence, 0 vorticity, and reverberation witfun the jet orifice,some flow fluctuation usually does occur. In some cases, this flow fluc-tuation is a significant source of noise (jet plaaes, turbines, etc., are

examples). In silencers, jet noise is generally substantially lowerthan precursor, blow-by, or blast noise. However, in some silencersthe jet noise becomes predominant. This is especially the case whenprecursor, blow-by, and blast effects are substantially attenuated,as in the Maxin and Sten gun silencers. The jet noise can also become

significant when the silencer baffle spacing is suc, that the baffledchamber resonance corresponds to the natural frequency of the dis-charging jet. In such cases both the amplitude and the dominant fre-quency of the jet noise can be substantially altered by changing thebaffle spacing within the silencer.

4

Presently the exact relationship between a sound signature andthe corresponding effects occuring in a silu-nced weapon j- only vaguelydefined. It is known, however, that generally the magritude andduration of any given sould pulse are primarily depend,-nt on thearea through which a quantity of propellent gas or air is dischargedto the atmosphere and on how this di'charge varies with time. *

In most silenced weapons the gas discharge area of interest isthe silencer muzzle opening. However, to predict the gas dischargefrom the muzzle prior to projectile exit, consideration must alsobe given to blow-by clearances, volume, and internal configurationof the silencer. The gas discharge rate of a pressurized chamber ortube is determined by both the discharge area and the stagnationpressure of the gas. 2 The stagnation pressure varies inversely withthe volume containing the gas. Thus, the silencer volume becomesa primary factor in determining the gas discharpe rate immediatelyfollowing projectile exit. Any significant change in the silencer vol-lime results in a corresponding change of the projectile exit soundpulse magnitude. In the case of system blow-by, the soundpulse is more dependent on the blow-by clearances, although oftenother factors also become significant. With the precursor wave,much lower pressures are encountered, and the more dominant roleis played by silencer length. **

The propellent gas pressure can Llso be reduced by heat ab-sorption. One method of effecting substantial heat absorption in thesilencer is to increase the contact surface between the hot propellentgas and the heat absorbent silencer material. The heat conductionis maximized by using materials with high heal. conductivity (a.g.,copper is good) and by exposing the gas to the heat absorbent mate-rial early in the expansion process when the temperature differentialis greatest. A good example of the heat absorbing technique isfound in silencers utilizing steel wools and wire screening. In mostcases, however, the heat absorption is limited by the short ballisticcycle times encountered in small armc weapons,

Another method of effecting large heat losses in the silencer isto introduce a foreign substance, preferably a highly volatile solidor liquid, into the propellent gas just prior to projectile exiR from the

*Appendix C"**Appendix D

5

silencer. The subste.nce evaporateo by absorbing heat from thepropellent gas thus reducing the internal pressure. Thepresumably successful application of this technique is to soak thesilencer wire screening in oil. Wate" is also usable, but may pres-ent corrosion problems. The general principle, although not thoroinghlyinvestigated in the past, seenms to have good possibilities.

Frorra the foregoing it becomes evident that the sourd signaturesof most conventional silenced weapons are primarily determined bythe silencer length, volurme, blow-by clearance, and heat absorbingcapability. Since in most silencers the heat losses are small, theusual silencer components (such as baffles, "devious passages."etc.) have their main significA-nce oniy in altering or reducing blow-by.

Several exceptional silencing techniques* deserving mentionmay now be added to the above described principles. H. P. Maxim,in the early 1900's, patented and manufactured a relatively auccessfulsilencer with specially formed baffles. These baffles chaineled theexpanding propellent gases into a peripheral motion within the silencer.The generated vortex reduced the pressure at the center, thus reducingthe propellent gas discharge rate from the silencer. Although to datethe principie lacks conclusive theoretical and experimental verification,superficially it seems sound. Except for the vortical gas motion, theMaxim silencer performed according to the principles previouslydescribed.

-Juring World War II, Germany deveioped several experimentalsilencers. One interesting version incorporated conical baffles, equallyspacedI along the silencer and inclined rearward. Although this tech-nique would not be expected to reduce the initial propellent gas die-ch,.rge rate after projectile exit, it does have a natural tendency to

reduce the precursor and the blow-by. This reduction can be attributedto the efficient inward reflection of all outgoing pressure waves withinthe silencer.

Some of the above German World War II silencers incorporateda flexible (sponge, rubber, etc.) disk at the silencer exit (patented1936 in Germany). The disk clcses off the internal silencer cavity un-

less forced open by the exiting p.ýrojectile, In this way the propellent gasis retained within the system uwtil it slowly seeps out. The rigidity ofthe disk ideally would be such that the precursor, blow-by, and ex-pandingblast pressures would not deform it and yet Lthe projectile could

*Appendix E

6

force its way through. A variation of the technique is to distributea series of these flexible disks throughout the length of the silencer.This design was utihzed in some versions of British World War IISten guns and Welrod pistols,

Most silencers discharge the propellent gas solely through thesilencer opening. A variation of this, not often encountered, isdischarging pressurized gas through the periphery of the gun barrelor silencer. Although the technique a.s described in some silencerpatents was probably unsuccessful, with proper gas discharge dis-tribi-ition and timing this silencer type could prove very effectiveacoustically.

A few of the early silenced weapon patents described mechanical

means for restricting the rapid propellent gas discharge after pro-jectile exit from the weapon. One of these prescribed the use of ametal gate to close the gun barrel immediately after projectile pas-sage. The gate in this case was to be driven directly by the propellentgas following the projectile. O~her patents described the sameprinciple, but added a side-branch, gas-driven piston to activate thegate. Another patent described a weapon in which the projectile wasdriven by a piston of slightly larger diameter. The piston was to bestopped at the chocked barrel muzzle while the p~rojectile woulct pro-ceed to exit. In this way the piston would trap the propellent gas insidethe gun barrel. The patent did not prescribe ai- expedient method fcrextracting the piston from the barrel. Still another patent describedan expansion chamber at the barrel muzzle which would allow expansionand eventual trapping of an expandable piston driving the projectile.The propellent gas was to be trapped behind the piston and graduallyreleasaed through small openings in the chamber. Although all of theabove techniques seem sound, more often than not they are plaguedby insurmountable design problems. Even if the above systems couldbe made operable, as described they would not be expected to effectany exceptional attenuation in noise.

DESCRIPTION AND EVALUATIONS OF

SILENCERS TESTED

An array r'f readil' available silencers and silenced weapons wastested at Frankford Arseaal. Since the inform-tion was collected over an

7

extended peri, ' of time, some ot the sound histories were recordedat distances other than five meters. All measurements werc madewith either a Bruel and Kjaer(B&K),!/4 in'h (Model 4135) or an Altec,1/2 inch (Model BRISO) condenser microphone. The microphone out-put w'as fed into an oscilloscope (Techtronix) and photographed forrecord. In a few cases the weapon st:tnd history was first recordedby a tape recorder ',Ampex 351) and then transferred to the oscilloscopeand the camera film. In each case sufficient cross-correlation existedbetween various transducers and recording techniques to render thepresented data, for all practical purposes, valid and reproducible.

Throughout the tests the -nicrophone, preamplifier, recordingequipment, and recording technique were found to have a paramounteffect on the validity of recorded sound data. Some microphonesystems were found to have insufficient response while others dis-torted the signal with resonance. eoth Altec and B&K microphonesystems showed a pronounced tendency to distort the signal whenmeasuring low intensity shock waves. They were almost completelyfree from resonance at higher sou.d le-vels. Although the specifiedfrequency responses of Altec andB&K microphones are, respectively,11,000 and 75,000 cps, both gave rel;tively comparable results forthe purpose at hand. The tap.: recoi:.:rs are generally not recom-mended for recording shock type sounds, primariJy because of theirslow response (usually not higher than 20,000 cps) and vulnerabilityto overloading. With care, however, useful data can be r-corded.

Another problem encountered during the tests was the soundreflection from the ground. Inc-ses where both the direct and re-flected sound signals were rec-xrded, no perceptible loss seemedto occur througl reflection from loose sand and sparse grass. Thereflected signal was simply slightly smaller in amplitude for havingtraveled a longer distance from the source. Consequently, it wasfound necessary to place the r.aicrophones andi weapon oufficiently farfrom the ground to insure receipt of only the primary signal. Thefurther fronm the gun the measurements were taken, the higher themicrophones had to be plactd off the ground.

Most silen'ers and silenced weapons tested were intended forstandard su.:sonic ammunition, availabl commercially. Somesystems, howe,.er, re-,-ircd special -:rducefd charge cartridges. Fortests, these rounds -.ere preared with appropriate type and quantityof propellant to yield pr jectile velocities substantially below theapeed of sou.ad. Since in some cases the projectile velocities intended

S8

by the system designers were not known, it is possible that the pre-pared and tested ammur.ition may have deviated slightly from that

intended. It is doubtful, however, that this factor could significantly- alter the sound results presented herein, Some systems, such as

the Sten gun, were designed for standard supersonic ammuntion. Inthese cases the barrel usually had propellent gas bleed holes to re-duce the internal pressure, thus reducing the projectile muzzlevelocity.

It is appropriate at this point to describe the methods wherebythe wea.pon's major noise constituents, listed with each of the follow-ing sound scope traces, were identified. In most cases the firststep consisted of examination of a sufficient number of the weapon'sscope traces to establish the recurrent character of the over-l weap-on noise. Next, scope traces were taken with the whole weapon. ex-cept the muzzle, w:apped with attenuating material (a suede leatherjacket was found to be a remarkably good attenuator). Noting

the noise components on the trace thus attenuated or completely e-liminated, positive identification was made of the weapon's breechnoise and the first noise emitted from the weapon 'nuzzle. Followingthis, scope traces were made with the weapon muz:le taped nver withheavy elastic tape. This determined the relative. time of projectile

exit from the weapon.

The mechanical noisen cdue to the weapon hammer and firingpin fall alone were determined by dry firing the weapon. In weaponswith detachable silencers, the precursar shock exit time was es-tablished from scope traces of the weapon fired without the silencer.Next, an impulse-time diagram was constructed fromn the scopetrace of the oerall unmodified weapon noise. This edtablished anapproximate relationship between ,he propellent gas dirchvrge historyof the weapon and antO the scope trace.

The times of the various r.oise-producir.g processes occur-ingin the weapon during the ballistic cycle were calculated from theknown or estimated projectile travel-time history. Analysis of allcalcula,,ed and experimentally established data led to idertificaticnof the major weapon r.oiue sources listed with the followrng sound

scope traces.

In practice, all sound measurements and loudness judgem-.nts

are made in the presence of sonie type if background noise. Althoughthe app-xrent loudness of A signal can often be altered substantially

by the background noise, presently there is no satisfactory means iorpredicting this masking effect. However, it is k.-iown that when thesourd pressitre level (SPL) of a continuous signal exceeds the SPLof background noise by more than 10 db, the effects of backgrox.,. Inoise, for all practical purpoat s, can be neglected. If the Jame

criterion iF assumed for transie.at noises, then masking of the w-.ap-on noise by the backgorund noise should become significant only whenthe background sound pressure exceeds about a third of the weaponsound pressure. Al: Frankford Arsenal sowud traces were made withthe background r-oise wvell besow this limit.

Caliber . 22 HI-stiandard Pistol/French Silencer

The "French" silencer is a re-cently manufactured item, designed

for a caliber . ZZ or a slightly larger caliber weapo)n. In all respectsother 'han ti-•t its baffles are not perforated, this silencer of Frenchorigin is Identical to a Parker-Hale "Sound Moderator" presentlybeing manufactured commercially in Bri:ain. History and exactorigin of the "French" silencer are unknown.

The all-metal silencer tested (Figures ý and Z) was adapted toa caliber . 22 Hi-stand,•rd semi-automatic pistol by threading thebarrel. Inside, the silencer contained a series of metal baffles,

spaced 0. 43 inch apart. The first baffle was located Z. 37 inchesfrom the gun barrel -ouzzle, preiu.-ably to reduce etresses on thebaffles and to provide an initial expansion chamber. The projectilepassage diameter throughout the silencer was 0. 28 inch. Outside,the silencer diameter and length were. respectively. 0. 94 and 7. 31Inches. Table I lists some of the more important physical and func-tional parameters of the Hi-standard pistol and the "French" si-lencer.

Figures 3 and 4 show scope traces of the sound pressur.:-timehistory of the pistol withokit the silencer tiring a Long Rifle cartridge.

Tl'etraceswverv reco:Jed five nieters frorn and direcly to the side of thepistol rni'zzle. The three primary acoustical effects - Primer initiation.precursor shock exit, and propellent gae blast - are distinctly visible onthe traces. The highest sound impulse and peak sound pressure level(136 db) were due to the propellent gas discharge occurring after theprojectile exited the harrel. The peak sound pressure level due to

exiting of• thl' precursor shock was 113 db. T1,e primer initiationsound pulse was appr.,ximately 9S db.

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ProjectileWeight (Long Rifle) 40 grDiameter 0. 2Z5 inVelocity (at silencer exit) 1050 fpsEnergy (at silencer exit) 98 ft-lbTravel at peak ballistic pressure (estimated) 0. 4 inchTravel in barrel 7. 0 inchTravel time in barrel 0. 65 rns (approx)Travel time in silencer 0. 55 me

PropellantWeight (double base. flake, web 0.003 in.) 1.7 gr (1O. 2 gr

primer)Chamber volume 0. 016 in. 3

Ballistic prem surePeak 24, 000 psiAt barrel muzzle (estimated) 1.000 psi

SilencerPassage diameter (for projectile) 0. 28 in.Weight 0. 25 lbFree volume 2. 38 in. 3

Pistol weig)'t (without milencer) 2. 75 lb

Time between precursor and projectile exits fromsilencer (estimated) 0.95 ms

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. The sound signature of a Hi-standard pistol with the Frenchsilencer and using A Lz'ng Rifle cartridge is shown in Figure 5. In thiscase the sotiu pressures were substantially lower tbar. withthe unsilencedpisntol. The firstdistinct soundl perceivedduring the firing cycle was a pulse

K (pt 1, Figure 5) generated about the time the firing pin hit the primer.

Since at this time four successive functions - hammer fall. firingpin striking primer. primer explosion, and gas lealrage rround thecartridge case - occurred, the exract source of the first sound pulseis not definite. However, experiments with other systems indicate"that, generally, by far the loudest pulses are generated by the gasleakage around the cartridge case and by the hammer fall. Thefiring pin striking the primer is generally somewhat louder in weap-ons r~ithout a hammer.

The next sound after primer initiation was the precursor waveexiaing irom the silencer muzzle. This sound 1.ulsi (Ot 2), becauseof its low amplitude, is barely distinguishable in the trace. Shortlyalter the precursor, the blcw.by pressure wave (generated by theleakage of propellent gases past the projectile) exited. Exit of thispressure wave gave rise to a pulse ot 117 dp peak SPL. The pro-jectile exited the silencer 0. 3 millisecond after thr- blow-by wave.Its exit was followed by the main efflux of gases, which resulted inthe positive pulse of 119 dp peak SPL. Following the projectileexit and initial gas efflux, the steady discharge of propellent gasesgave rise to turbulence which, combined with reverberations withinthe silencer, generated a prolonged noise (pt 5) of approximately105 db peak SPL.

Sound signatre of the caliber . 22 Hi-standard pistol vithoutsilencer, firing a SFhort cartridge, is shown for reference in Figure6.

Caliber . 22 Silenced Hi-standard Pistol

Duri.ig World War II, the U.S. Infantry Board establishedinterest in silenced weapons. 37 A variety of weapons, including thesilenced c.aliber . 22 Hi-standard pistol (Figures 7, 8, and 9. andTable II), were given consideration. It w.as concluded that all si-lenced weapons were bulky and still detectable at close ranges. Be-cause of low lethality, it is doubtful i; the Hi--tandard pistol describedherein found very wide application.

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ProjectileWeight (Long Hfle) ýO -Diameter 0. Z25 In.Velocity (at silencer exit) 930 fpsEnergy (at uilencer exit) 75 ft-lbTravel at peak ballistic pressure (estimated) 0. 4 ;n.Tr&vel in barrel 6. 2 in.Travel time in barrel 0. 65 ms (epprox,Trave1 time in silencer 0. 2Z ma

PropellantWeight (double base, flake, web ,.. 0. 003 in.) 1. 7 gr (+ 0. 2 gr

primer)Chamber volume 0. 016 in. 3

Ballistic pressurePerk Z4, 000 psiAt barel muzzle (estimated) 90 psi

SilencerPassage dianeter (for projectile) 0. 234 in.Weight (excluding gun barrel and Distol) 0. 63 lbFree volume

Around gun barrel (including barrel holes) 1. 84 in. 3In front of gun barrel 0.76 in. 3

Wire mesh volumeRolled (around gun barrel) 0. 79 in. 3Discn (front of barrel) 0. 35 in. 3

Gun barrel and pistol weight 2. 37 ib

Silencing of the H!-Ptandard r'atoJ has been accomplishedessentially by drilling the barrel and enclosing it in a silencing tube.The barrel has fotxr longitudinal rows of "bl-ed" holes, 0. 125 inchin diameter aad spaced 0. Z50 inch apart. The primary function oithe holes, is reduction of the ball'stc pressure which, in turn, alsoreduces the velocity of a supersonic Long Rifle cartridge below the

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The silencing tvbe surrounds and -xtends beyond the pistolbarrel. At the rear it is attached to the threaded receiver extension,while at the front it terminates with a threaded cap. Inside, thetube contains a roll of brass wire tieshr surrounding the barrel anda stack of vyire mesh discs extending beyond the barrel muzzle.. Thewire screening is presumably intended for cooling of the propellentgases. Projectile passage through the front portion of the silencingtube is 0. 234 inch in diameter. The silencing tube diameter andlength (beyond gun barrel) are, respectively, 1. 0 and 2. 5 in.

Figure 10 chows the sound pressure-time history of the silencedHi-standard pistol. The sound trace, Like that of the French silencer,was taken five meters to the side of the pistol muzzle. As can be seenfrom the scope trace, the pistol'smain sound sources were: primerinitiation (pt 1, Figure 10), bleed hole blow-by (pt 2), and projectile exi(pt 3). The primer initiatioai pulse, which was predominatly due topropeilent gas leakage around the cartridge case, had a peak SPLof 98 db. The next sound pulse (pt 2) was gererated when the blow-byoccurring through the bleed holes exited from the muzzle. Although

this sound pulse had a relatively large impulse, its peak SPL wasonly 101 dh. Shortly after, the blow-by wave, originated at the gunbarrel muzzle, exited. This event occurred almost simultaneouslywith the projectile exit. The combined effect of blow-by and gasdischarge following the projectile exit resulted in a positive pulse(pt 3) €-f 113 db peak SPL. Following this, several sound pilses occurred(pt 4) due to propellent gas discharge turbulence and reverberationswithin the eilencer.

The magfitude of these sound pulses varied from round to round.In the majority o! ct.ses it was somewhat lower than that of Figure 10.The general negati-,e trend of sound pressure after sound nulse (pr •)was more consistent. reprei.enting the eventual decrease of propellentgas discharge from the weapon. In Feneral, the relatively unclutteredsound scope :race of the silenced caliber . 2Z pistol correlateC4 wellwith its quiet performance.

Caliber . 22 Silenced AA1 Experimental rest Fixture

The A.I caliber .. Z silenced test fixture (Figures 11, 1 Z, 13,and Table 111) was desifn.-• by Aircraft Armaments, Incorporated.in 1965, The study "LLs conducted as part of a Frankford Arsenalcontract issued :o investigate unconvertional uso of small arms,

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ProjectileWeight 40 grDiameter 0.2 5 in.Velocity (-c sileacer et) 990 fpsEnergy (at silencer exit) 88 ft-lbTravel at peak ballistic prseuurp (estimated) 0. 4 in,"Travel in 'barrel 6, q in.Travel time in burrel (estimated) ?, 72 ms

PropellatWeight (double base, flake, web - 0. 003 in.) I. 7 gr (+ 0. 2 gr

privner)Chamber volume 0. 016 in.

Ballistic pressurePea3 24. 000 pi.At barrel muzzle (estimated) 130 psi

SilencerOutmxdn diam.ater 1. 0 in.Length 6. 5 in.Weight (excluding action and gun barrel) 0. 5 lbFree volume (including gun barrel holes) 4. 69 in. .

Total f'i.xtfe and sisencer wo.ight 1. 5 lb

TheAAl fixture ic essentialya, a.liber. 22 single shot rifl#- ,ctionwith a 7-inch barrel. The barrel has a total of 28 holes of vraiottsdiameters driled along its length. The first fotir holes are erclosedby a section of a Negator spring, presumably to givo adaptabilityto both the Short and the Long Rife cartridges. Surrounding the bar-rel is a silencing tube which forms an expansion space for the pro-pellent ga•, escaping throtigh the barrel bleed holes. The expansionspace is divided by six baffioe which isolate each set of bleed holes

28

and thus prevent exceusive blow-by. Some chambera surrounding thebleed holes contain i"loed steel wire mesh, presumably intended tocuoo the expanding gases.

The perforrmance of the AAI silen•.ed Yixture is airnple in prin-ciple. As the projectile travels down the barrel, the prnpellent gasbleeds off through the barret holes and egpands intn the &pace aroundthe gun barrel. The expansion of propellent gas is accompanied by areduction in the ballistic pressure behind the projectile. By the tin-Aethe projectile exits from &he barrel, the ?ropellent gas pressure hasbeen reduced to ýhtt dictated by the total expansion space (and slightheat absorption). The lower pressure behind the projectile at exitresults in a lower initial propellent g.s discharge sound pulse.

The advantage of this design is that with proper sizec, num~ber,and plac.ment of bleed holes, both the p.recursor and the blow-bysound pulsea can be minimized. The system's disadvautages are: (I)the premature propellent gas bleeding results in a reduction of pro-jectile velocity; (2) the eventual abrupt uncorking of the barrel isaccoustically undesirable; anid (3) the prolectile (especially a leadprojictile) in susceptible to deformation and erosion by propellentgases if bleeding is accomplished too abruptly or w.hile the gas pressureis still high.

The sound pressure-time history of the AAI tent fixture is shownin Figure 14. The trace was recorded fi-ve meters directly to the sideof the wsapon. As with the silerced Pi-standard pistol, the first soundpulse (pt I, Figure 14) recorded corresponded to the time of firingpin fall. The peak SPL of this pulse was 93 db. Since the time betweenthis eveat, primer explosion, and gas leakage around the cartridgewas small, the three eve.ets are not readily distinguishable on thescope trace. However, the pulse due to leakage arouiad the cartridgeseems to be in the vicinity of 103 db.

The seccnd aad londest sound pulse (pt 2) was due to gas leakagefrom the joint between the silencer tube and fixture breech. The gasleakage, occurring as soon as the projectile vassed the first set of bar-rel bleed holes, resulted in a peak SPL of 1I1 db. This sound pulseco:ald be eliminated by a tighter fit between the tube and breech.

The next pulse (pt 3) was due to exiting of the precursor war.e andthe propellent gases which foumd their way through the bleed holes aheadof the projectile. This souad pulse was relatively small, with a peak

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SPL of 201 db. Mhortly alter the precursor and blow-by. the pro-jectile exited. This resulted in the main efflux of gases from the

muzzle and the consequent blast pulse (pt 4) of 114 db peak SPL.

Following this initial blast pulse were the various sound pulses emittedfromra the muzzle due to the reverberations within the barrel and the

silencer. The last sound pulse (pt 5) was a ground reflection of the

pulse due to gas leakage at the silencer tube base. As can be seen,reflection of the sound pulse from the ground (sand and spFrse grass)occurred with almost negligible attenuation.

Caliber . 22 Hi-standard Pistol/ FA Silencer

The experimental silencer shown in Figures 15 through 17 was

designed by two Frankford Arsenal employees in 1967. It evolvedconcurrently with the availability of low cost porous metal machiningstock. The porous metal manu'acturing techniqjzes, whic'h only re-cently were refined, consist of casting the molt4'n metal iver a saltconfiguration and dissolving the salt after the r.etal hardens. Pres-ently, a nu-nber of metals can be cast into almost any porosity,density, or shape. The silencer doscribed herein is probably a fairrepresentative of its t:,pe.

The caliber . 22 Frankford Arsenal silenctr vs tested with thesame Hi-standard pistol used for evaluation of the French silencer.It is all-aluminum, and measureo 1. 4 inches in diameter and 6. 5 inchesin length. The silencer is machined from stock whtich is partially solidand partially porous (Ftee Figures 15 through 17 and Table IV), Outside,

tht6 porous section of the silencer is wrapped with electrical tape, whichlimits the propellent gas discharge to onl'/ the 0. 23 in. diameterprojectile exit at the silencer muzzle. Inside, the silencer consistsof three ch'nmbers of different lengths and diameters.

The oucrtanding characteristics of the caliber . 22 FrankfordArsenal silenzer are small weight, low manufac.:uring cost, and rel-

atively quiet acoustical performance, The undesirable features ofthe silencer are its bulkiness and high erosion rate, Other physicaland functional characteristics of the tested silenzer arelistedin TableIV.

The general acoustical performance of the Frankford Arsenalsilencer can be surmised from the sound scope trac shown • i Figu:re 18

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Projectile

Weight (Long Rifle) 40 grDiameter 0. 225 in.Velocity (at silencer exit) 1050 fpsEnergy (at silencer exit) 98 ft-lbTravel at peak balliatic pressure (estimated) 0. 4 in.Travel in barrel 7.0 in.Travel time in barrel 0.65 ms (approxýTravel time in silencer 0. 47 ma

PropellantWeight (double base, flake, web -. 003 in.) 1.7 gr (+ 0. 2 gr

primer)

Chamber volume 0.016 in. 3

Ballistic pressurePeak 24. 000 psiAt barrel muzzle (estimated) l. 000 psi

SilencerPassage diameter (for proJectile) 0. 23 in.Weight 0. 47 ibTotal free volume 5. 6 in. 3Total pore volume 4. 9 in. 3

Mean pore diameter (approx) 0, 04 in. "

Porous alumwium density 0. 043 lb/in. 3

Pistol weight (without silencer) 2. 75 lb

Time between precursor and projectile exis.from silencer (estimated) 0. 90 mn

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(see Figures 3, 4, and 6 for sound scope traces 0o the pistol withoutsilencer). The main sound sources of the silenced pistol were primerinitiation (pt 1, Figutre 18), blow-by (pt 3),and gas discharge followingprojectile exit (pt 4). The noise due to precursor (pt 2) was relativelyinsignificant. The primer initiation Pound pulse (as previously de-scribed) occurred due to gas leakage around the cartridge caqe. .'hepeak SPL of this pulse was 103 6b. The next and largest sound pulsewas that due to the exit of propellent gases which by-passed the pro-jectile. This pulse had a peak SPL of 108 db. The projectile exitedapproximately 0. 4 ms after the klow-by. The gas efflux followingthe projectile exit gave rice ýo a sound pulue of 100 db peak SPL.

In general, the sound aignai'ure of the caliber . 22 pistol withFrankford Arsenal silencer could be described a3 a relatively mild,mtffled hand clap. The systern siuzxLded somewhat quieter than Clesilenced Hi-standard pistol.

CUIlber . 30 M1903 Ri/le/Maxim Sileacer

The all metal caliber . 30 MCxxim silencer herein described wasdesigned by H. P. Maxim. The frst versins of this U. S. silencerwere patented and manufactured comriercially in 1909. At the time,the use of the Maxim silencer wa-s considered by the Army, andissue of two silencers per plat0oon wat recommended for trainingrecruits. However, due to the baliist;tc crack of the supersonicround. the Mi-xim silencer, as vell ac several other designs, nverfound wide application. it is doubtful if, at that time, the use of amodified (subsonic) cartridge was given much consideration exceptfor special missions.

The Maxim silencer version recently tested at Franldord Arsenal(see Figures 19 through ZZ and Table V) is the "Miodel 15" supposedlyissued to National Guard units during World War 1. It Is approximately9 inches long and 1 Inch in diameter. The silencer is 0. 16 inch eccen-tric with respect to the rifle bore. It attaches to the military Sp:'i-ag-field rifle by an end nut and two tapering half-sleeves. The (ron. riflesight must be removed aid replaced during the mounting ope'atibn.Inside, the Maxim silencer is compo.sed of an initial expansion yhamberfollowed by 19 equally spaced baffles., The bafflee are indented rear-ward and off-center from the Ellez.cer and the rifle boriv axes.

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Weight .lou.c) 175 grDlaxnatez 0. 309 :n,Velocity (at silencer eit', 1050 fpcEnergy (it slleree-. exit) 431" ft-lbTravel at peak ballistic pressure (estmrnated 0.4 in,Travel in barrel 22. 0 Zn4.Travel time in barrel 2.. 3 ma (appI ox)Travel tirne in silencor 0. 56 me

PropellantWeight (M9 dcubl base, flake, .ub 0. 003 in.) 7.6 gr (+ 0. 5 gr

pr•imer)•:bamber volume 0. 30 in. .

B3allistic pres'eurePaak Z0, 000 psiAt barrel muzzle ((stirnated) 1,000 psi

SilencerP,-isarge diametcr (for projec'iPie) 0. 375 in.Weig,)t 0.63 lb

Free volumi- 4. 0 in. 3Ojxtxi(.e dia•reter 1. 0 in.Lengtf. (beyond gun ba rrel) 7. 0 in.

SRife weight (v.ichout silen•ce.) 9 lb

Time between precui sor and projecLile exitsfrom qilencer (enti-ated) 1. 44 rns

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The Maxim Wsencer baffle conflgura'ion induces the gases,propagati;ag down the silencer, intor a vortical spin. No data seem tobe available on the acutai effectiveness oif the 1.'finciple. However, isIs •.oncelvabke that pressureb at the kilencer projectile passage couldthua be subatantially reducrd. The Maxim silencer's acoustical Per-forms.nce (Figure 25) isrmuchbettev thai would be expected from i aclearances, volurne, and length alono. Thus, some effectivenessntzst be attributed to the silencer's eccerxtricity and the askew baffies.Howevir. the value of the vortical spin principle still 4 emains qaes.tionable.

11gure 23 shows the sound pressure history of the caliber , 30 MI ?03fle withoul. the silencer, using a subsonic cartridge. As zan Lie seen

from the scope trace, the main sound sources are prucursor shock(pt 2, Fig%,re 23) and propolent gas discharge following the projectileexit (pt 3). The corresponding SPL, of these pulses are, r,ýspectively,119 and 137 db five meto.rs to !he side of the weapon.

The sound prescure-' _-i history of the M1903 'rifle with theMaxim silencer and subsonic cartridge is shown in Figurer _4 and 25.`,he system's main noise sources are primer Initiation, precursor shock.blow-by, and propelleic gas dimcharge after projectile exit. The perimerWnitir.tion noiseofrorr, firing pin fall to the first muzzle soundrs" shown in

Fig s 24. The absence of the usually high initial positive sonid pulsesu .- sts that gas leakage around the cartridge case is very low andthat moot oi the system's initial noise is mechanic¢l. Sound pulsesdue to the blow-by end the propellont gas discharge after projectile

iti are shown more d&atiuctly in Figure Z5. Here the blow-by andgas divcbarge pulses aye, respectively, 102Z ant 112 db peak SPL.Following these pulses, there is a prolonged, seemingly random.noise of appro.,iriately 10Z db -eak SPL due to gas discharge turbu-lence and revei berat;ono ins.ie tht silencer.

The general oouwd history and apparent loudness of the testedai-dm siieucer tre comparable to the better silenced systems. Thio

i1 especially sifkafico't in view of thi relativei- hiZh projectile cnergy(431 ft,.1b) sad vel•zity (1OS0 fps). Combining this with the sileucer sadaptbility tW "ada: ,aonu, Its relatively small size, r.nd itscoustruction (requiring no mruinteaance or replacer.neut of parts), theWW I Maxim silencer Is oua of the better item w tested at FrankfordArsenal.

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Caliber . 30 Silenced MI Carbine -

The silcrced Ml carbine (Figures 26 and 27 and Table VW) wasdeveloped in Enfield, England, about 1945. It is believed to have beendesigRed for the Office of Strategic Services. The carbine is manuallyoperated and takes standard supersonic ammunition. Because of itsbulkiness, manual feeding, and no. too impressive acoustical performance,it is doubtful if the weapon was widely utilized.

Since standard supersonic ammunition was to be used ia the siiencedcarbine, seven holes of 0. 125 inch diameter were drilled in the barrelciore to th-e breech. This allowed the gases to be bled off through theholes, with a consequent reduction in ballistic pressure and projectilemuzzle velocity. The original barrel length was also reduced to teninches, presumably to minimize the final length of the carbine. Thecarbine's silencer surrcu,,ds and extends seven inc/;es beyond the gunbarrel. Inside, the silencer has a aeries of conical baffles, plsitioredthroughout its whole length. The overall length and diameter of thesilenced barrel are 17 and 1. 4 in., respectively.

Sound pressure-time history of the tested carbine. live inetersto che bide of the weapon, is shown in Figure 28. The main constitu-eAls o: the noise are: primer initiation (pt 1, Figure 28), bleed-holeblow-by (pt 2). gun barrel muzzle blow-by (pt 3), blast immediatelyfollowi:ng projectile exit (.gt 4), and continuous noire emitted fromsilencer after projectile exit (pt 5).

The primer initiation noise (barely visible on the trace) wasappro imately 94 db peak SPL and was primarily due to the hammerfall. T'he gas blow-by around the curtridge case seems relativelyInsignificant.

Following primer initiation, the first significant sound pulse(pt 2) was caused by tht exit of the pressure wave generated by thegases finding their way out tlrough the barrel bleed holes. This wasa posi~ive cound pulse of 112 db peak SPL. rho secondary blow-oy,which occurred at the gun barre! muzzle, exited the silencer approxi-nately 0. 6 zr s after the bloed hole blow-by. This generated a postivesound pulse of 122 db peak SPL.

The projectilh, followed the secondary blow-by by about 0. 4 ms.The immediate accoustical effects associated with the projectileexit ( pt 4) are barely distinguishable from the ficope trace. This isdue to the masking effect of reverberations within the silencer and

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--Projectileveight 108 gr

Diaamet~er 0. 306 in.Velocity (at silencer exit) 1058 ipsEnergy (at silencer exit) 270 ft-lbrravel at peak ballistic presauxe (esti~nated) 0. 5 in,Travel in barrel 9. 2 in,Travel time in barrel 1. 30 me (approx)Travel tinhe in silencer 0. 56 ma

PropellantWeight (WC820 double base,, spherical granulation

0.013 by 0,0009 in.) 13 gr (+ 0.3 grprimer)

Chamber volume 0. 062 in. 3

Peak ballistic pressure 31. 800 psi

SilcncerPassage diameter (fcr projectilej 0. 375 in.Free -volume 10. 3 in. 3

Carbine weight (withomt magazine)Silenced 6 75 lbStandard unsilenced 5 lb

Time between precursor and projectile exitsfrom silencer (estimated) 0. 41 ms

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diaeharge turbulence occurring at this time. An approximate valueof 119 db peal SPL, was assigned to the projectile exit pulse. Follow-ing the projectile exit from the silencer, there wvae a continuous noiseof about 118 db peuk SPL. Tbas high frequency noise, which again canbe attributed primariily to internal reverberations, per'sisted foriveral milliseconds. It is superimposed on a gradual trend into thenegative sound pressure region. This, of course, signifits theeventual decrease of gas diacharge frcm the weapon;

To a subjective listener, the firing of the silenced carbine noundedlike a sharp hand c:lap followed by a distinct hissing sound.

Caliber . 32 Silenced Sleeve Gun

Little is known about the origin and history of the silenced sleevegun. It bears close similarity in design and workmanship (Fig~xres 29through 32 and Table VII) to the caliber . 32 Welrod pistol. The sleevegua is a singlo shot item, requiring considerable time for reloading.To reload and cock the weapon, the three rearmost threaded sectionshave to be disassembled. Independent operations are required forrechambering the cartridge and resetting the firing pin spring, Theweight (1. 7 1b) and general configuration of this gun suggest that itwas also intended ior use as a club.

Firing of the weapon is accomplished by moving a latch towardthe weapon mur.zle. A rod, attached td the latch and running alongtbh top of the sleeve gun, releases the plunger holding the firing pinat the rear of the gw%. At the biite, tLe sleeve gun is provided withan eyelet, prestnnably fora string to support the weapon in a coatsleeve.

The internal configuration of th& sleeve gtu, except for dimensionis,is exaf;tly the same as that of the caliber . 32 Welrod silenced pistol. *

The 3. 25 inch gun barrel contains a series of Z0 holes, 0. 063 inch indiamy-eter, positioned in five rifling groove&. The holes lead into anexpansion chamber formed by the tube surrounding the gun barrel.The tube also extends beyond the gun barrel muzzle by 2. 85 inches,thus formin3 the forward silencer section. Inside. 'he silencer sectioncontains a series of metal and rubber baffles which provide the si-lencing effect.

*See Figure 35.

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ProjectileWeight 77 grDiameter 0. 315Velocity (at eilencer exit) 700 fpsEnergy (at silencer exit) OZ ft-lbTravel at peak ballistic pressure (ectimated) 0. 35 lii.Travel in barr-l 3, A5 in.Travol time in barrel (estiniated) 0, 54 Ta

Travel tine in silencer 0. 34 ms

PropellantWeight (Norma, ACP. double bate, web - 0. 003 in.) .3 gr (+ 0. 3 gr

primer)Chamber O.0•6 .0n.

Peak ballistic pressure *4,000 psi

Projectile passage dlamteterIn steel baffle 0. 38 in.

In old rubber 1affes 0. 25 in. {approx)In new rubber b,,.ffles X-suit

Free volumeAround gun barrel 1. 18 in. 3

In front silencer portion 1. 2 in. 3

Totml weapon weight 1. 7 lb

57

"When ex:amined, the rubber baffles of the sleeve gun hereindescribed were already old so that passage through them was ap-pro mrnately 0. 25 inch in diameter. Waen new, the rubber bafflespr,.bbably ccmpletely c.losed off the silenccr cavity. Therefore, arecord was also made with a new baffle containing only an X-slitthrough the center,

Figure .3 shows and identifies the various iiound constituentsof the tested caýliber . 32 sleeve gun with old baffles. Tha first smallsound pulse on tMe trace (pt 1. Figure 33) corresponded to the time ofprimer initiation. This pulse, as well as other small pulses immediatelyfollowing it, was approximately 87 db peak SPL (unpublished data),and was primarily due to firing pin fall. Vas leak-age around thecartridge case seemed negligible.

The next sign.ficant sound pulse (pt 2) was emitted from thesilencer muzzle. It was identified as the pressure wave due to thepropellent gases exiting through the bleed holes and finding theirway ahead of the p-ojectile, The peak SPL of this pulse was 118 db,the same as that for the caliber . 32 Welrod pistol.

The blow-by occurring at the gun barrel mizzle inside the si-lencer followed the bleed hole blow-by by about 0. Z5 ms. This pulsewas 114 db p ak SPL. The projectile exited approximately 0. 3 mslater. The efflux of propel.ent gas immediately following the pro-jectile resulted in a positive pulse (pt 4) of 126 db peak SPL. Thepositive souned pu~lse 0, 2 me after pt 4 was due to re-verberation in-

sidb the weapon.

The sound szope trace of the sleeve gun with new rubber bafflesis shown in Figure 34. As can be seen, practically all noise precedingand following projectile exit was eliminated by the new baffles. Also,the projectile noise was reduced to IZ0 dp peak SPL. In-general. thesleeve gun with old baffles sounded lik- a somewhat loud srap. Firedwith new baffles, it soundd likewire snappy. bt• substantially quitter.

Caliber . 32 Silcnced We'rod Pistol

The caliber . 3Z pistol (7igures 35 and 36 ikvd Table VIII) bearsclosw resemblance to the 9 r•vn Welrod pistol* developed ir, Britian

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ProjectdieWeight 77 grDlimater 0.315 in.Velocity ("• silencer exit) 770 fpsE£nergy ýat silencer exit) 102 ft-lbTiaveL in barrel 3. 9 in.Travel time in barrel (estimated) 0. 54 meTravel time in silencer 0. 43 ms

PropellantWeight (Norma, ACP, double ba3e, web 0.003 in.) 3 gr (+ 0. 3 gr

primer)Chamber volume 0.0 6 in. 3

Peak ballistic pressure 1.4,000 psi

Projectile passage diameterIn steel baffle 0. 375 in.In old rutber baffle (when tested) 0. 25 in (approx)

Free iolumeArotud gur. barrel Z. • in. 3

In front silencer portion 2. 5 in. 3

Total ;rstol weight (unloaded) 2. 5 lb

63

during World War It. Externally, the prirnivy difference between thetwo is that the caliber . 32 is somewh-%t smaller and do,•e not have atrigger guard. The Welrod pistol is orte of thc_ few weapons specif-ically designed to be "sClent. 11 It had been provided with a suitablesilencer and a relatively quiet breech mecharnism. Although its clipithe pistol handle) holds eiglit rounds, the pictol requires slow manualreloading for each shot.

Internally, the caliber , .32 Welrcnr pistol consists of a metal tube

surrounding and extending beyond the plsto barrel. The barrel hasa series of 20 holes (0, 062 inch in diarr~etk-r drilled around its pe-riph-iry. The holen are positioned in the five rifling grooves andlead to the surrounding expansion chamber, This chamber is sep-arated from the front silencer secticn by a L dffle which has 12 nioles(0. 062 inch in diameter;. The silencer sectiovi, extending beyond thebarrel muzzle, is four inches long and contains a series of metal andrubber baffles. The rubber baffles are spaced intermittently betweenthe metal baffles (Figure 35). The projectile passage diameter in thexteel baffles is 0. 375 inch. The passage diameter in thz old rubberbaffles, when tested, was approximately 0. V; inc'l: when new, therubber baffles probably completely closed off the silencer interior.

Figures 37 shows and identifies the various sound pulses ger-erated by firing the caliber . 3Z Welrod pistol. The main aoundpulses were due to primer initiation (pt 1, Figure 37), bleed holeblow-by (pt 2), and projectile exit (pt 3). The high SPL (--12 db)and positive nature of the first sound pulse (pt ý) ideixtify it at thatcauned by gas leakage around the cartridge case. The blow-by wave(generated by the propellent gas by-passing the projectile throughthe barrel bleed holes) exited approximately 0. 4 ms later. Thisgave rise to the pulse (pt 2) of 118 db peak SPL. The blow-by waveoccurring at the gum barrel muzzle exited from the silencer approx-imately 0. 3 ms after the bleed hole blow-by. From the scope trace,ic is seen that this blow-by is almost insignificant. The last &ndLUrgest sound pulse, with its poak SPL of 1Z2 db, was due to thegas discharge immediately following the projectile exit. Followingthiu, there was a prolonged high frequency noise of about 104 db peakSPL due to turbulence and reverberations within the system.

In general the caliber . 32 Welrod sound signature could be de-scribed as a sharp snappy crack.

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9 mm Silenced Welrod Pistol

The 9 mm Welrod pistol, except for size, is externally verysimilar to its caliber . 3Z counterpart. Internally, however, thetwo pistols are quite different (see Figures 35, 36, 38, 39, arA Table

IX). The 9 mm Welrod barrel consists of two sections, front andrear. The rear portion contains the gun barrelwhich has sixteen0. 052 inch diameter bleed holes at its breech end, The gun barrelis surrounded by a tube whichb totther with the threaded frontbushing, form, s an expansion chamber for the gases escaping throughthe bleed I.oles. The front portion of the pistol barrel is essentiallythe weapon's silencer. It attaches to the piesol by means of a threadedbushing. The inside of the silencer Ptction contain. a series ofmetal, rubber, anid felt baffles separated by a perforatted, spool-likesteel spacer. The passage through the steel baffles and spool isapproximately 0. 43 inch in diameter.

The pistol examined at Frankford Arsenal contained threeflexible baffles .. two rubber and one ftt. The projectile passagethrough these baffles was approximately 0. 35 inch in diameter. Whennew, however, the flexible baffles .robably completely closed offthe silencer cavity; therefore, reý_ords were also made vith newbaffles containing only an X-slit. Not knowing the condition of thetested weapon, rmist firingi -were rrmade with a reduced charge car-tridge (described in Table IX).

Figure 40 shows the sound pressure-time history of the 9 ramWelrod pistol without the forward siltncer se;.:tion and firing the re-duced charge round. The first noise detectable (and bazely visibleon the trzice shown) occurred at about the time the firing pin hit theprimer. This noise (pt 1, Figure 40) had a peak SI-L, of approximately105 db, and was due to gas leakage around the cartridge case. Thenext sound pulse (pt 2) was due to the pre.cursor shotuk exiti-g fromthe gun. The high SPL of this pulse (131 db) suggests a possibilityof gas leakage pist the projectile. Any bypassing of the propellentgas naturally reiniorced the precursor, giving rise to the high SPL.The last pulse (pt 3) was due to propellent gas disclarge immediatelyfollow*ng the project-Ae exit. rhi.s pulse had a peak SPL of 131 db,the isame as that of che precursor puls~e.

Thu sound performance of the 9 mm Welford with the nilencercontaining old bafflen is shown in the sound pressure-time tra.-ce ofFigure 41. Here the r-ain noise constituents were primer initiation

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TABLE IX. 9 mm Siienced Welrod PistoL

Prot ectileWeight 115 grDixnieter 0 357 in.Velocity (at silencer exit) 6-40 fpsEnergy (at silencer exit) 106 ft-lbTravel at peak ballitic pressure (estimated) 0. 4 in.

Travel in ba.rrei 4. 7 in.Travel time in gun oarrel (estimated) 0. 71 msTrcvel tim-. in atlencer 0. 60 ms

PropellantWeight (M9, double base, f!ake, web ., 0,003 in.) 3 gr (+ 0.3 3r

primer)Chamber volume 0.038 in. 3

Ballistic pressurePeak ZZ. 400 ps.;At first hole (estinated) 10.600 psiAt gun barrel muzzle (estimat td 2-00 psi

SilencerWeight (front portion) 0.63 lb 1Free voicne arounI gun barrel 2. 3 in. 3

Free volume in iront portion 4. 5 in. 3

Projectile passange diameterSilencer spool 0.43 in.in old rui,,:er baffles 0. 35 in. (apprcx)Through rew rubber baftles X-slit

To:al pisto) weight (with the silencer' 3. S lb

Time between arenursor and projectile exitsfrom silencer :estimated) 0.91 rr.s

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(pt 1, Figure 41p, precursor exit (pt 2, blow-by e:dt (pt 3), andprojectile exit (pt 4). The relatively low SPL ,- 105 dbl of primeri.t.ation suggests that leakage aro-ncd the cartridge case was much

rmaller tvan that of the caliber . 32 Welrod. The precursor sound [pulse had a peak SPL of approximately IlI -1b. The blow-by wave, rwhich originated from the propellent gases bypassing the pro-jectile in the spocl spacer, constituted the second loudest soundsource of the system. This blow-by sound pul.e (pt 3) had a ?eak a

SPL of approximately 119 db. The last and largest soune putse(pt 4) originated at the time the projectile %xited from the silencer.It had a peak SPL of 124 db, and was due to the abrupt pror-ler.t

gas discharge following tne projectile exat.

A record of the silenced Welrod with nz,.w rubber bafflas. firinga reduced ch:.rge cartridge, is shown in Figure 4V. A s can be seen,the primer noise was nmaifected, but the precursor and blow-bywere praciically elimninated by the new baffles. Also, the projectileexit pelse wa& reduced to 1 •G db p.ak SPL. Fig-are 43 ahows thetrace of toe silenced Welrod with new baffl~sx firing a standard 9 rr•'NATO cartradge (silencer muzzle velocity - 930 fps). IPre the peakSPI, of thr projectile exit was 125 db.

In general, the 9 mn. Welrod with old baffles sounded similarto, altho,.%gh somewhat louder than, thke caliber . 3Z Welrod .istol. Withnew baffles it sounded appreciably quiter than before.

9 mm Silenced Sten Submachine Guna

The silencc I Sten submachine guns (Figure 44) were firstdeveloped and manufactured in Britain during World War U. Theywere successfully atsed by both the British Commandos and the guer-,rillas operating behind German lines. A few of the silenced Stens

eventually found their way into German handa but, contr•:y to strongrecurnm-rendations by some, the German High Command did nvt adoptthe Sten fox general use.* More recently. silenced Stervs were re-portedly used by Allied troops in Korea.

Basically, the silenced Sten (designated Mark IIS) is a modifiedversion of a standard unsilenced Sten submachine gun. The mod-ification consisted essentially of reducing the bolt weight, shortening

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the bolt spring, and substituting the replaceable barrel with a si-lenced one. Since the new barrel reduced projectile velocity belowthe speed of round. the bolt modifications were necessary to insureproper weapon operation and to maintain the rate of fire at standard450 rpm. Some modified weapons reportedly had their breech in-sulated with acoustical material, this to atteuuate the weapon's me-chanical noise (Figure 45). Many versions of the silenced Stun barrelare known to have been developed. Two types, both similar, weretested at Frankford Arsenal.

Silenced Stan Darrel, Type I

The Type I silenced Sten barrel (Figure 46) consists ea-sentially of a drilled length of stan'iird 4 inch long gun barrel and asurrounding silencing tube which extends beyond the gun barrel muz-:le. The gun barrel has six holes (3. 11 inch in diameter) located0. 72 inch from the initial projectile base position, and opening intothe expansion chamner surrounding the gun barrel, The early bleed-ing of propellent gases is primarily intended to reduce the velocityof the standard supersonic round below the speed of sound.

The front end of the silencing tube forms the seconda,-yexpansion chamber, which a s divided by 30 straight, equally spaced,metal baffles. The first and last baffles (0. 25 inch thick) consist ofstacked wire screen discs. The passage through the baffIcs providesthe projectile with a diametral clearance of 0. 040 inch. Outside, thePilenced barrel is partially covered by asbestoo rope. electrical tape,and canvas cover to protect the hands from the tube which becomesaxcessively hot with automatic firing. The overall silenced barrel is13 inches long ane I. 5inches in diameter. By comparison, the stan-dard unsilen-.ed Sten barrel is only 6 inches long. Some of the moresignificant physic~al and functional parameters of the silenced Stenwith the Type I barrel are listed in Table X.

On firing, the forward (and rearward) motion of the Stenbolt terminates with a considerable slap. Thid in-plct of bolt againstbreech and the consequent vibration of the weapon's various •omponentsgenerated pruolnged noise of about 100 db peak SPL, lasting a fewmilliseconds (Figure 45). To avoid the overshadowing effects ofmechanical noise, the Frankford Arsenal sound tests were conductedwith the silenced Sten barrels held and fired in a special, relativtlyquiet, single shot test fixture (Figures 47 and 48)_ Since t!Oe rnecha•tica)noise of the fixture is relatively low. the rccorde,-2 icfope traces ea-sentially contain only the system muzzle noie.

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TABLE X. 9 rnm Sileaced Sten Submachine Gun, Type I Barrel

PrOj-1ctile

We:ght 115 grDiameter 0. 356 in.Velocity (at silencer nxit) 1000 fpsknergy (at silencer exit) 258 ft-lbTravel at peak ballistic pressure (estimated) 0. 3 in.Travel in barr4l 4. 25 in.Travel tia-n' in barrel (estimated) 0. 42 meTravel time in silettcer 0.71 ms

PropellantWeight(WCC-6I02,doublebase. weo,0. 003 i, ) 6 gr (4 0. 3 gr

primer)Chambar volurne 0. 038 in. 3

Ballistic pressurePeak 31,000 psiAt barrel muzzle (estimated) 250 psi

Silencer CharacteristicsPassage diameter (for projectile) 0. 50 in.Free volurne ir front silencer portion IA. 0 in. 3Free volume around gu.n barrel 4. 4 in, 3

SIlenced barrelWeight 2. 25 lbLenght 13 in.Diameter 1. 5 in.

Standard Sten gun barrel length 6 in.

Total weight of sile-iced Sten submachine gun(without magatine) 7. 7 lb

Time between precursor and projectile exits

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barrel~fired with the test fixture is shown in Figure 49. Time coi re-

lation of the trace with the various functional effects occurring in the*

2ystern during firing Indicuted that the five principal noise sources

were: primer initiation (pt 1, Figure 491, precursor wave exit (pt 2),blow-by exit (pt 3). projectile exit (rt 4), and reverberation and jet

noises after projectile exit (pt 5).

The primer initiation noise started and continued after

the firing pin hit the primer. The high frequency, long duration, and

low amplitude indicate that it was primarily mechanical in nature.

The peak SPL of this noise five meters from the system was appr,)x-

imately 93 db. The prect-rsor wave formed in the gun barrel exited

from the silencer approximately one r-s after the fi.ing pin bottomed.

The precursor sound pulse, although not very distinct, seems to have

had a peak SPL of about 94db. The blow-by wave, caused by gasss

by-passing and the projectile in the silencer, exited 0. 3ms later.

The sound pulse (pt 3) Jue to this blow-by had a peak CIPL of 104 db.

The projectile exited approximately 0. 4 me after the blow-by wave.

The efflux of gases following the projectile etit was fairly mild

since the event was barely distinguishable from the secondary acous-

tical effects (such as reverberations and turbulence) occurring at

this time. The noise generated during this event seems to have

been about 106 db peak SPL. Following the projectile exit, tnh.re

was a relat-vely random prolonged noise generated by the reverber-

ations inside the silencer and zhe jet turbulence. The sequence and

magnitude of the various sound pulses of this noise are incons, itent,

varying from round to round. In gener-, for any one given round

the mnaximum and average peak SPLs of this noise are in the vicinityof I1 2 db and 104 db, respectively.

Although the silen':ed Sten barrel in somewhat bulky, in

general it compensates for this by very good acoustical performance

and long service life. To a subjective listener, tle system sounded

as an abrupt initiation and gradual cessation of a relatively mild hiss,

Compared to other silencers and silenced barrels with respectable

energy oututs, the Sten was one of the quieter systems tested 4tFrankford Arsenal.

Silenced Sten BarrelL Tye II

Externally, the Type I and Type UI silenced Sten barrels

are almost identical. The two barrels are also similar in principle;

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Ihowever, each contains a slightly different set of internal components(Figured 46 and 50 and Tables X and XI). The Type 11 is disting ,ishableprimarily in that its gun barrel is slightly shorter and contains two

sets of bleed holes; its -.ctal baffles (fewer in number) are somewhat

conical in shape; and, at the forward end, it holds three felt washers.

In the barrel tested at Franklord Arsenal, the front conicalbaffles had been modified previously, as shown in Figure 50, pre-sumably for experimental purposes. Acoustically there seems tobe HUith. apparent reason for this modification; if anything, it made!the system slightly louder. Originally, acoustical performance ofthe two barrel types was probably very similar.

Figure 51 showR and identifies rhe sound constituents oftha silenced Type U Sten barrelsfired with the test action shown inFigure 48. The trace was recorded five meters directly to the sideof the weapon. The first distinct noise recognizable on the trace(pt 1, Figure 51) was a sound generated approximately when the firingpin hit the primer. This series ofpulses, with its relztively low peakSPL of 93 db, was essentially mechani-al in nature. The next soundpulse (pt 2) was the first noise emitted from the silencer muzzle.This pulse of 101 db peak SPL was genexated by the blow-!ýy occurringthrough the gun barrel bleed holes.

The rext souri pulse (pt 3) corresponded to the timý: %'hengun barrel muzzle blow-by exited the silencer. This sound pulsehad a peak S/PL of 104 db. The next, and highest, sound pulse (pt 4)was generated by the exit of propellent gas which bypassed the pro-jectile through the modified front baffles. Exit of this blow-by wavegave rise to a pulse of 113 peak SPL. The projectile exited approx-

inately 0. Cl mna later.

The initial efflux of gases following the projectile exitresulted in a positive pulse (pt 5) of 104 db peak SPL. Followingthis, the steadily discharging gas gave rise to urbulence which,

combined with reverberations within the silencer, generated a pro-longed noise (pt 6) of approximately 100 db peak SPL, Characteris-tically, this noise was of random nature, varying fioro round tor'ound.

To a subjective lis ener, the Type II Sten sounded likea clap-initiated, gradually diminishing hiss. In general, it seemedcomewhat louder than the Type I Sten.

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TABLE XI. 9 mm Silenced Sten Submachine Gun. Type II Barrel

Pr"ojectileWeight 115 gr

Diameter 0. 356 in.

Velocity (at silencer exit) I000 fpsEnergy (at silencer e:it) 258 ft-lbTravel at peak ballistic pressure (estimated) 0. 3 in.Travel in barrel 3. 1 in.Travel time in barrel (estimated) 0. 3 msTravel time in silancer 0.91 ms

PropellantWeight (WCC-6102, double base, web 0, 003 in.) 6 gr (+ 0. 3 gr

primer)Chamber volume 0. 038 in. 3

Ballistic pressurePeak 31,000 psiAt barrel muzzle (estimated) 400 psi

Silencer CharacteristicsPassage diameter (for projectile) 0. 50 in.Passage dianmeter in old felt baffles (when tested) 0. 3 in.Free volume around gun barrel 2. 7 in. 3Free volume in front silencer portion 13. 0 in. 3

Silenced barrelWeight 2. 5 lbLength 13.5 in.Diameter I. 5 in.

Standard Sten gun barrel length 6 in.

Silenced submachine gun weight (without magazine) 7.9 lb

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9 mm P38 Walther Pistol/AAI Silencer

The 9 trnm AAI experimental silencer (Figures 52 and 53 anoTable XII) was manufactured '3y Aircraft Arrnmrnents, Inc. aboutthe same time as the caliber . 22 silenced AAI tesr fixture (seepage 21). This silencer is adaptable to a P38 Walther pistol by re-moving the front sight and securing the silencer to the barrel muz-zle with an adaptor sleeve. Although it is rather bulky and acous-tically not too irmpressive, its data are deemed useful for comparisonwith other silencers and silencing fixtures.

The 9 rmm AAI silencer is essentially a simple~haffled, expansionchamber, 5 inches long and 2. 5 in:hes in diameter. The steel silencerhousing holds eight baffles and nine spacers, all aluminum. Seven ofthe equal chambers formed by the baffles contain loosely packed Pteelwool, removal of which does aot see-n to affect the system acoustically.There is a :'ubber diaphragnm with an X-slit at thia silencer muzzle,presumably to restrict gas flow. At Frankford Arsenal this diaphragmrequired frequent replacement as i'. was easily destroyed by the ex-iting projectile. Later it was found that the diaphragm had littleacoustical tffect even when new, probably because it was too thin.

The outstanding features of the AAI silencer are its vezy largevolume (19 in. 3) and the surprisingly l.rge projectile clearances (a0. 5 inch diameter passage for a 0. 35 inch diameter projectile). Thefollowing sound data are from the firings made with a special subsoniccartridEe (see Table XII).

Figure 54 shows the sound pressure-time history of the 9mrn P38pistol without the silencer, recorded 10 meters to the side of thewerpon. The first sound pulse (pt 1, Figure 54) was due to the pre-cursor exit from the gun muzzle. This pulse had a peak SPL of 127 db.The projectile exited the gun muzzle approximately 0. 4 ms after theprecursor. The accompanying propellent gas discharge gave rise to* sound pulae (pt 2) of 139 db peak SPL. The positive pulie (pt 3) isa ground refleftion of the blast pressure wave.

The sound signature of the P38 pistol with the AAI silencer isshown in Figure 55. The rmaain noise constituents of the system wereidentified as: primer iritiation (pt 1. Figure 55), precursor exit(pt 2), blow-by exit (pt 3),andprojectile exit (pt 4). The first significantnoise during firing was that due to gas leakage around the cartridgecase. The peak SPL of this noise was approximately 99 -b. The next

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Projectile 1 rWeight 115 gr

Diameter 0. 356 in.

Velocity ( at silencer exit) 925 fpg

Energy ( at silencer exit) ZZO ft-lbTravel at peak ballistic pressure (estimated) 0.4 in.

Trav21 in barrel 4. 35 in.

Travel time in barrel 0. 46 ms (approx)

Travel time in silencer 0. 43 ms

PropellantWeight (M9. double base, flake, web 0.003 in.) 3 gr(+0. 3gr

prime )Chamber volume 0. C;38 in. 3

Ballistic pressurePeak ZZ 400 psi

At barrel muzzle 1,800 psi

Silencer

Passage diameter (for projectile) 0.50 in.Weight 3 lb.

Free volume 19 in. 3

Pistol weight (without silencer) 2. 1 lb

Time between precursor and projectile exitsfrom silencer 0.43 ms

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sound pulse (pt Z) was generatedwhen the precursor e~ited from thesIlencer. Its peak SPL was 105 db. The blow-by wae generated atthe gun barrel muzzle exited from the silencer after the precursor.This blow-by pulse, with its peak SPL of 120 db. represented thesystem's loudest effect. Tie projectile exited about 0. 2 rn& after theblow-by w've. Gas flow at the silencer exit evidently was altered littleby the projectile since the event is not diocernable on the scope trace.This, of course, was to be expected with the large blow-by clearancesand volume. To a subjective listener, the system sounded unquestion-ably loud.

9 mm Walther MP1 Submachine Gun/West German Silencer

re MPK silencer (Figures 56, 57. and 68) was reportedlydeveloped in West Germany sometime after 19463, when the 9 mm MPKsubmachine gun itself was introduced. Although somewhat bulky andinternally elaborate, it is ruggedlyconstructed, well finished, andreadily adaptable to a standard MPK weapon. The construction of thesilencer, its size and acoustical performance suggest that it was built Ias an experimental model-shop item. I

haternally, the MPK silencer (Figure 56) consists of a 10 inchlong by 2 inch diameter expansion chamber containing an elaborateassortment of geometrically complex tubes, vanes, and cones. Exceptfor two steel end pieces and the steel turbine-like vanes, the silenceris made entirely of aluminum. Beginning at the rear, the silencerstarts with a simple 1. 5 inch long expansion chamber, followed by atubular srool.out side-vaned at the rear and closed at the front. Thesteel vanes forming one end of the spool are brazea to the alumintuntube. After the spooi come two ccnes, an expansion chamber, andanother cone.

All Frankford Arsenal sound tests on the MPK were madewith special rounds loaded for subsonic velocities (Table XUI•. Thesound history of the MPK without the silencer is shown in Figure 59.The weapon's rrmain nots-, like that of most other unsilenced systems.was du.e to the prccursor wave and the projectile exit blast. The two

Positive Plser fivt rieerao to the side of the MPK were, respectively,131 and 140 db peak SPL.

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ProjectileWeIght 115 grDiameter 0. 356 in.Velocity (at silencer exit) 1000 fpsEa.ergy (at silencer exit) 255 ft-lbTravel at peak ballistic pressure (estimated) 0. 4 in.Travel in barrel 6. 32 in.Travel time in barrel (estimated) 0. 62 msTravel time in silencer 0. 79 ms

Propell.atWeight (M9, doublebase, flake, web . 0. 003 in.) 3 gr (+ 0. 3 gr

pi imer)Chamber volume 0. 038 in. 3

Ballistic pressure

Peak2240psAt barrel muzzle (estimated) 1.400 psi

Silencer IPassage diameter (for projectile) 0. 41 in. , 0. 44 in. *

and 0. 55 in.Weight 1. 5 lb (approx)Free volurmit 15.0 in. 3

Unoilenc~ed aubmachine gun weight (withoat magazine) 6. 2 lb.L

Time between precursor and projectile exits fromOilencer (eb;imated) 0.69 me•s

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Although not visible in the trace of Figure 59, the MPK has arelatively loud, prolonged, mechanical noise. This noise is dueprimarily to the forward slap of the bolt against the breech andconsequent vibration of the weapon's mechanical components. Thesound trace of the weapon, fired dry. witliout a cartridge, is shownin Figure 60. The peak SPL of the MPK's mechanical noise wasapproximately 106 db five meters irom the weapon.

The sound history of the silenced MPKhfiring a subsonic car-tridge.is shown in Figure 61. The system's first significant sound(pt 1, Figure 61) corresponded to the time of pirmer initiation. Thefirst positive pulse of this sound (approximately 106 db), five metersfrom the weapon, was due to the forward slap of the bolt againstthe gun breech. Approximately 0. 2 ms after the bolt bottomed, therewas a second positive pulse of 114 db peak SPL due to rearward gasleakage around the cartridge case. Following primer initiation camethe firut noise emitted irorn the silencer muzzle. This was a pulse(pt 2) of 108 db peak SPL due to the exiting of the precursor wavegenerated in gun barrel. The blow-by occurrirng in the silencer ex-ited from the muzzle approximately 0. 4 ms later. This gave rise toa positive pulse (pt 3) of 116 db peak SPL. The projectile exitedabout 0.4 me later. This generated the system's largest pulse - 118db peak SPL. Following this there was a series of smaller randomsound pulses due to reververationm inside the silencer.

Figure 6Z showc, essentially, only the muzzle noise of thesilenced MPK. The record was obtained by wrapping the weaponwith a suede coat. The effect can be seen most readily in the barelyvisible primer initiation noise (pt 1, Figure 62) and the more clearlydefined precursor pulse (pt 2).

In comparison to other systems, the silenced MPK soundedsomewhat louder than the 9 mm Stensi and quieter than the caliber . 3Zand 9 mm Welrods. Qalitatively, the MPK sound signaturc couldbe described as a somewhat muffled cOap, immediately followed bya diminishing hiss.

Caliber . 45 Silenced M3 Submachine Gun (Figure 63)

1Bel Laboratories Silenced Barrel

During World War I1, Bell Laboratories investigated si-lencing of various weapons, including the caliber 45 M3 submachine gun.

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designed and presented to the Infantry Board for evaiuation. Conclu-sions from the tests were that the silenced M3 was quiet, but stilldetectable at close ranges. A thousand silenced barrels were re-portedly b'ilt and supplied for use by the Office of Strategic Services(oss).

The Bell Laboratories silenced barrel consists essentiallyof a drilled gun barrel and a silencing chamber surrounding and ex-tenuP'g beyond the gun barrel muzzle. Along its length, the gun barrel Lhas 48 holes (0. 25 inch diameter) which are positioned in four straightrows. During firing, some of the gases are bled off through theholes, with a consequent reduction in the ballistic gas pressure andthe projectile muzzle velocity.

The ailencing chamber is composed of two sleeves ofdifferent lengths and diameters, connected by means of a reducingbushing. The rear sleeve encloses a roll of wire mesh which sur-rounds the drilled gun barrel; the forward sleeve, which extendsbeyond the gun barrel muzzle, contains a stack of wire mesh discs.The projectile passage thrcugh the wire mesh discs is 0.05 inchin diameter.

The mechanical noise associated with firing the silencedV.3 submachine gun is substantial, if not dominant. As with the Stengun, it was found more realistic to evaluate the silenced M3 barrelwithoat the overshadowing mechanical noise. Concequently, thesound results eescribed herein were obtained with the silenced bar-rel held in a special aiingle shot test fixture. * The following soundrecords were rec, rded by an Ampex 351 tape reco-der before beingtransferred to the oscilloscope and the camera film.

Fig'-ir.- 67 shows a scope trace of the sound pressure-timehistory of a standard caliber . 45 M3 barrel (7. 5 inches long) firedwith a test fixture. The trace was recorded ten meters to the side ofthe weapon. The two prominer.t sound pulses on the trace were dueto exitirg of the precursor wave (pt 1, Figure 67) and the gas dis-charge following the projectile exit (pt 2). The two pulses were,respectively, 115 and 130 db peak !:)PL,

Sound signature of the Bell Laboratories silenced bar-reland tent fixture is shown in Figure 68. The main sound pulses were:

*See Figures 71 and 72

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TABLE XXV. Caliber . 45 M3 Submacbine Gun/BeU LaboratoriesSilenced Barrel

ProjeceileWeight 235 grDiameter 0. 450 in.Velocity (at silncer exit) 768 fpsEnergy (at silencer exit) 3]0 ft-lbTravel at peak ballistic pressure (estimated) 0. 22 in.Travel .n barrel 7. 4 inTravel time in barrel (estimated' 0. 95 meTravel time in silencer 0. 69 ms

PropellantWeight (HPCI, double base, ilake, web- 0. 003 in.) 5 Zr (+ 0.4 gr

primer)Chamber volume 0.061 in. 3

Ballistic pressurePeak 20,000 psiAt gun barrel muzzle (estinmated) 200 psi

SilencerPassage diameter (for projectile) 0. S0 in.Free volume around gun barrel 7. 2 in. 3Free volume in front portion 2. 5 in. 3Volume, rolled wvre mesh (brass) 2. 9 in. 3Volume, stacked wire mesh discs (brass) 2. 8 in. 3

Silenced b~rrelWeight 2.63 lbTotal length 14. 2 in,

Standard M3 barrelWeight Z. 5b lbLength 7. 9 in.

Standard M3 3ubmachine gun weig)-t (without magazine) 8. 1 lb

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primer initiation (F•t 1, Figure 68), bleed hole blow-by exit (pt 2),gun barrel muzzle blow-by exit (pt 3), aid projectile exit (pt 41. Thebleed hole blow-by (pt 2) and the gas discharge following projectileexit (pt 4) constituted the main noise rources of the system. Bnthpulses had a 107 db peak SPf,. The gun barrel muzzle blow-by re-sulted In a sound pulse (pt :;j of 101 db peak SPL.

Although the Bell Laboratoricz' silenced barrel reducedprojectile velocity of the standard M3 submachine gun from 920 of770 fps, tho. projectile muzzle energy still remained a respectable310 ft-lb. This is only slightly less than the onergy of a caliber .45pistol and 50 ft-lb more than the energy of the tested 9 mm silencedSten gun.

To a subjective listener, both systems (Bell LaboratoriesM3 and the 9 mm silenced Sten) sounded comparable in loudness.However, each weapon had its own characteristic sound signature -

the M3, a mild clap; the Sten. a distinct hiss. A disadvantage ofthe M3 is that the wire mesh requires periodic cleaning and replace-ment.

AMF Silenced Barrel

The AMF silenced M3 barrel (Figures 69 through 72 andTable XV) is an experimental item manufactured in the 1960's byArnericaa Machine and Foundry Company (AMF). It utilizes a 5. 6 in.long gun barrel and a 1. 25 in. diar0-eter silencing tube which surroundsand extends 9 inches beyond the gun barrel. Whereas the space sur-rounding the gun barrel is not ntiLzed, the fro.0 portion of the tubeforms the system's silencer. This front section is filled through-out its length with closely stacked wire mesh discs, separated byfive irregularly positioned rubber discs. In the silenced barreltested at Frankford Arsenal, the projectile passage thro-agh therubber discs was approxmately 0. 5 inch in diameter. )riginally,these discs probably partially or completely closed off the silencerinterior. The gun barrel of the AMF system is 2 inches shorter thanthat of a standard M3 weapon. This, however, res.ults in only aslight reduction in projectile velocity.

The AMF silenced barrel was tested at Frankford Arsenalwith a single shot fixture, shown in Figures 71 and 72, Figure 73shows the scope trace of the sound pressutre-time hiatory of the 5. 6inch

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TABLE XV. Caliber . 45 M3 Submachine Gun/AMF

Silenced Barrel :4Proje tile

Weight 235 grDiameter 0. 45 in.Velocity (at silencer exit) 910 fps

Energy (at silencer exit) 435 ft-llTravel at peak ballistic pressure 0. 22 in.Travel in barrel 5. 6 in.Travel time in barrel 0.85 msTravel time in silencer 0.83 me

PropellantWeight (HPCI. double base. flake, web 0.003 in.) 5gr (+-0. 4gr

primer)Chamber volume 0. 061 in. 3

Ballistic pressurePeak 20. 000 psiAt barrel muzzle 1, 600 psi

SilencerProjectile passage diameter in wire mesh d'iscs 0. 50 in.Projectile passage diameter in old

rubber discs 0. 50 in.Free volurme (fornt of barrel) 4.9 in. 3

Free volume around barrel (unused) Z. 9 in. 3

Volump. stacked brass wire mesh and rubber discs 4. 5 in. 3

Silenced barrelWtight 2.5 lbLength 15. 1 in.

Standard M13 barrelWeight 1.25 lbLength 8. 0 in.

Standard Mi submachine gun weight(without magazine) 8. 1 lb

Time between precursor and projectile exitsfrom silencer (estimated) 0. 5f ms

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long gun barrel without a silencer. The trace was recorded tenmeters to the side of the weapon. The two prominent sound pulseson the trace were due to precursor wave exit (pt 1 . Figure 73) andgas discharge following the projectile exit (pt 2). The correspondingpeak SPL'o of the two pulses were 113 db and 130 db.

Sound pressure-time history of the AMF silenced M3barrel (with old rub'-er baffles) is shown in Figure 74. The firstsound recorded upon firing the system was generated at the time ofprimer initiation. The low peak SPL ("-93 db) of this sound indicatesthat it was primarily mechanical in nature. The next sound pulse(pt 2, Figure 74) was generated when the blow-by wave exited fromthe silencer. This wave, formed by gases by-passing the projectile,remulted in a peak SPL of I 27 db. Projectile exited from the silencerapproximately 0. 65 ma later, giving rise to the positive pualse ipt 3)of IZ db peak SPL.

In general, firing of the AMF silenced barrel was ,:har-acterized by a relatively shaip crack, Perhaps only slightly quieterthan that of a standard caliber . 22 Short pistol. Better acousticalresults would possibly have been realized if tl~e rubber discs werenew. However, the system's loudness would probably still be limitedbyf noise due to abrupt emergence of the massive projectile. (See dataon 9 mm Welrod.)

CONCLUSIONS

The more important physical, functional, and acoustical dataof the tested silenced and uncilenced weapons are tabulated in TableXVI. The peak SPL's of the various pulses in this table were takenfrom the preceding sound scope traces. In cases where the soundscope trace was recorded at a distance other than five meters, thedata were extrapolated for comparative purposes.

Although in most weapons the nmajor :ound pulse was generatedat tl'e time of projectile exit, there were aome weapons (such as thecaliber . 2Z Frankford Arsenal silencer, caliber . 30 carbine, etc.)which gnerated the largest pulse becaust of blowy-bv. Some weapons

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(with gun barrel bleed holes) generated a large sound ptulse due tobleed hole blow-by. In all weapons except the caliber .45 Btli Lab-oratories silenced barrel, this pulse -rax secondary in magnitude.

The primer initiation peak SPL was found to vary 'rom weaponto weapon. There were even 3ubvst.,%tial differences betv ean similar"weapons. However, since in most cases the largest primer initiationpulse was due to gas leakage aroune the c5,rtridge case, subitantialdifferences in SPL could be attributed to miniute differences in car-tridge chamnber clearance or simply to dirt accumulation in the weapon.The highest primer initiation SPL was 'hat of tCe 9 mm MPK (114 db)0The caliber . 3Z sleeve gun had the lowest initiation pulse with a peakSPL of only 87 db.

For some of the silenced weapons, sound scope traces weretaken at various distances (1, 5, and 10 ineters). Although the dataare not included herein, it ir wort.h mentioning that with sonme silencedweapons the peak SPL readings at I and 5 meters were found to differby asmuchas 18 db. This is a 4-db greater attenuatioi than woud beexpected from a simple spherical expansion. From 5 to 10 meters,the peak SPL of some weapons was attenuated by nearly 7 db instead ofthe normal 6 db. It was also noticed that wi~h distance, vome changsooccurred in the general shape of the various sound siLLals. In eachcase many of the short sound pulses tended slowly to coalesce, thusdefining more and more clearly such pulses as precursor, blow-by,etc.

The above effects can be attributed to the fact that high soundpressures propagate at a slightly faeter velocity than lower soundpressures.* Although the phenomenor, may bear little significancein general acoustics, in Frankford Arsenal tests it was found suffi-cient to induce a slow, but noticeable, change in the shape of thevarious major pulses toward that of a balanced N-wave.

Throughout the sound tests, efforts were made to note how eachweapon sounded to a listener, particuarly in terms of quality and re-lative loudness. These Impressions were later compared with thecorresponding sound scope traces. Although, at most, only severallisteners were involved, the consensus is nevertheless interesting.Almost invariably sound signatures with one or several shock pulses

*See Appendix C

122J

sounded sharp and snappy; the signatures containlng a. is ge numberof pulses or simply mcre 'hash" also sounded snappy, but lesssharp. more prolonged, more muffled, and more rarairn in quality.Sound signatures which were predominatly "'hash" (such as those o(the Sten, Maxim, and carbine) sounded like an abrupt initiation of ahiss (or hish). All sound signatures cortaining distinct and Lecog-nizable shocks seemed more piercing.

Although the quality of each sound tignruture was definitely rec-ognizable. the primary factor determining the relative loudness wasfound to be the signal's peak SPL. * Whether by coincidcnce or design.the weapons with higher peak SFL a1most invariably sounded louderand -1ftore perceptible. This, of course does not discount the factthat there may be other dcmirant factors affecting a given weapon'sdetectability at large distances. As an. example one could considerthe faster attenuation of short pulses with distance.

Compiled experimental sound data i icate that Zhe better si-lenced systems registered a peak SPL of approx~mately 110 db fivemeters from the weapon. In most weapons, the main sound sourcewas the abrupt discharge of propellent gas. In some weapons (thosewith flexible baffles) the noise due to gas discharge wta relatively low;howuver, the abrupt projectile emergence at the muzzle generated anoise just as unde3irable. The precursor wave of an unsilencedweapon generated a peak SPL in the vicinitr of 120 db. Most of thestraight-through silenced weapons tested attP.nuated the precursordown to about 90 db. The me,..hanical noise was found to devend onsystem design. In some of the qieter weapons, mechanical noise wasin the vicinity of 90 db.

Evaluation of the compiled experimental and theoretical dataindicates that a siienced system quitter than the weapons tested atFrankford Arsenal is feasible. Howcver, a system with noise levelbelow 90 db L.t five meters will most likely evulve gradually and onlywith a fuller understanding of the noise-generating mechanisms.

RECOMMENDATIONS

1. Conduct analytical design of an optimum silenced small armswe-pon based on experi'inntal and anaiytical data generated to date.

*See Appendix F 1Z3

2. Continue otnalytical study of noi. se-generating and attenuatin&,mechanisms in small arm weapons.

3. Acoustical evauation of small arm weipons should be basedon identification and interpretation of individual noise sources de-termined from osciil',.cope traces of the overall weapoij sound history.reak sound pressure level should be established as a factor of primary

-.gnificance.

IZ4

I

APPENDIX ABALLISTIC CRACK FIELD

Whin a supersonic projectile exits an unsilenced gun barrel.the uncorked propellent gases generate a spherically empanding blastwave. The wave initi•lly bypasses the projectile; however, dissipatingrapidly. it slows downto aimost sonic velocity and is overtaken bythe projectile within & maater of a few feet from the muzzle, Later.in the free far field, the initial projectile lag is oversbadowed by thelinear geometric exp.nsions, and projectile, muzzle blast, and bal-listic crack acquire app.roximately the proportion&a relationship shownbelow.

KJZM, MLAST

SUZUE BLAST bA.sSZDOVER BY¥ BAUISTIC

-,5ALLJS(!C CIACZ

Here .he sound fil.Id consists essentially of ballistic crack, muztileblast, and mutzlc blast passed over b-. Lallistic crack. The acous-tical significance of ballistic crack and .•uzzla blasthavt been pre-viously considered.,* It only remains to mention that ade section ofmuzzle blast wave, hiving been passed over by the ballistic crack,

*See Appendix C &.d Referent, 46,

- - • . .. • • ,i i l • - • . . . . .i _ , . ..ff . .. .. . II I - I2 5. .

essentially suffers only slight refraction and scattering by turbu-

lence.

In the far field. th* ballutic crack cone is nearly tangentlal to

the b2ast wave aphere.

The angle between the ballistic wave envelope &nd the projectile

trajectory depends solely on the projectile velocity-46 It is expregsee,

by:

where M = mrojectile Mach No.

The azimuth angle from the weapon to the tangency point of

blast and ballistic wave envelopes is expressed oy:

The plot of the ballistic crack field hall-angle. 9. is shown below.

9090

.j 80

•"3o

20

126

Thus, it is seen that~with the usual supersonic projeclile velocities,the ballistic crack is confined to approximately a 130" cone to thefront of the waapon. The cone increases to 160' with projectileMach number of 6. At Mach 1. 5, the cone decreasen to about 100,

Aid at Mach I it vanishes altogether.

The above data find application when silencing a supersonicweapon. Thus0 although the silencer will effectively attenuate muzzlebiast the usually loudt and far raaging ballistic crack will still persistwithin the dcfined frontal cone. To the side and the rear %ill beheard the i'o.newhat weaker, spherically expanding ballistic crackreflectitig from the weapon.

127

APPENDIX B

SUBSONIC PROSECTILE FLIGHT NOISE

Subsonic projectiles generate noijse in flight. Although thisnoise is much quieter than that of supersonic projectiles, it can bequite loud an.' detectable at large distances from the projectiletrajectory. To the side of the passing subsonic projectile, one hearsthe characteristic swish; first increasing, then diminishing it in-tensity. Although thisnoise, likeall turbulence-initiated noises, canhave a seemingly rardom quality, in the far ficId it is generally foun.dto be periodic. Its frequency depends primarily un the flow velocityand the diameter of obstruction in the flow; however, as will be seen•several other factors must also be given consideration. A typicalsubsonic, small calibe,. flat based projectile geuerates about 95 dbpeak SPL at 10 meters from its trajectory. In comparison, themore streamlined projectiles are generally found substantiallyquieter.

The basic noise-generating mechanism of subsonic projectilesconsists, briefly, of the following. Througho'At the projectile flighta. certain amount of air within tht turbulent boundary layer followsthe projectile. (See simplified figure below.)

- -1 , - DETACEMh VO1M!XV 10

"ýTURMILVIT BOXJNDA&Y IAYER

The velocity differential between the surrounding air and the airtraveling with the projectile generates shear forces which acceleratetl.e air within the boundary layer into a vortical spin. The attaehcdspherical vortex size increases simultancouwdy with incr-ased spinuntil the vortex is finally warhed downstream. Thus. the amount ofair traveling with the projectile decreaseea and the process repeats.

128

The energy of the attached spherical vicrtexZ7 propagating at

the velocity of the projectile is

Ev b3 Po Vz (1)

where

b = vortex diameter, projectile wake diameter;

po = air density;"V = projectile velocity.

The energy expended by the projecti!e to generate a single vortex is:

Ebf. Cb ( 4n 0 V ' (2)

wherepVZ

Cb = projectile wake area drag coefficient. Pb/--;

f = proJectile vortex shedding frequency.

Upon equating the above two equations, it is found that

L f 10 b(3)

Thus, the projectile vortex shedding frequency acquires the familiar

form of Strouhal frequency. f = (const) V/b. For flat tailed projectiles,

Cb has a typical v&lue of 0. 2. When the flow is fully attached, which

is the case with projectile boat tail tapers not exceeding about 15,

the wake diameter c i generally be assumed equal to that of the pro-jectile base flat. If the flow separates before the tail end, then the

wake cross-section area can be taken av approximately the averageprojectile area between tail and point of separation.

Representing the sound generating projectile as a movingmonopole source, the far field sound pressure to the side of tne pro-

jectile becomes

4~r d(42

129

where

r = distance from projectile trajectory;-dtm,- time change of air mass now rate from and toward

projectile.

The sound pressureas a function of time.cin be represented by

P r Pm sin Zvrft (5)

where

Pm = ptak sound pressure:t = time.

Combining Equations 4 and 5 and integrating, the air mass flow rateat the projectile is found to be represented by

cos ZnTft. (6)

Integration of above eq.ation over a time period of half a cyclo yieldsthe periodic change in air mass attached to tbR projectlie as

M = Zrpm (7)iVf

Thus, the peak sound pressure as a function of frequency and period-ically transferrable mass becomes

Prn = W

Butthe transferred rmass a't the projectile is that ot the sphericalvortex; i. e.,

M b3 (9)

130

Combining Equations 3. a. and 9, the peak sound preasure generatedby the subsonic projectile is found to be

49P2 b o.•V

Pm- 4t20 rb (10)

Thue. knowing the projectile uhape and velocity, Equation 10 may beused to estimate the peak sound pressare. Comparison of suchestimates with experimental data available to date* from a fewvariously shaped projectiles Indicated reatively good 3greernent.

Unpublished Frankford Arsenal data

131

w4

APPENDIX C

GUN MUZZLE BLAST

In the far field, a noise gencrating tube can often be treatedas a simple acoustical monopole source; 2 6 . 3 4 that is, its sounddiverges as a symmetrical sphere. Ithis is most readily borne ouftby the schlieren photographs of discl-arging shock tubes and abruptlyuncorked pressurized cylinders (i.-Acluding small arm weapons). 5- 18

Each of these cases aLkncst invariably shows the initial shock. expandingspheical.ly frormi the tube mouth. It may naturally be further inferredthat the air or gas behind the expanding shock also moves sphericallyaway irorn the cource.

Physically, a moaopole sotirce can be envisioned as a sphericalbaloon expanding or contracting uniformly in all directions, thus gen-erating sound pressureswhich also diverge unif3mly in all directions.The far field cound pressure for such a source is given by

P 41r T(1)

where

p = far field sound pressure0 = ambient air density;r = distance from source;

Q = volume of ambient air being displaced by source;t = time,

Algebraic manipulation and integration of the above equation yields

0 dQfpdt = ýo ' Q-

where

dtQ= instantaneotis air volume displacement rate at the source;

cdt umu1tive area under the sound signal's pressure-time trace.

132

With a scurce (such ae a pornus sphere, a nozzle, etc.) of constantdischarge area emitting gps, the air displacement de.pends on the quan-tity of gar. being discharged and on how this gas expands from dischargeto atmospheric pi essure. In cases of interest the expansion processis generally very nearly ioentropic. Thus, the instantaneous airvolume displacement rate can be exrressed by

"a- Ao t Aut (3)

where

Pt absolute pressure of gat at discharge;

Po = ambient air pressure:y = gas ratio of specifL,- ),eats;At = gas discharge area;ut = gas flow velccity at discharge.

The sound signal pressure-time area becomes related to thesource gas flow pararneters :y

jipdt = iL' .... (4)

Thus, it is seen that the cnlmulative sound signal im, pulse is directlyproportional to the volumetric air or gas flow rate at the source.That is, the positive and the negative sound pulses represent, re.-spectively, an increase and a decrease in gas flow rate. Farther,since a given increase in gas flow must eventuaUy be followed by anequal decree re in gas flow, it follows that a transient iignal mustnecessarIly consist of both a positive and a negativc portion. Each,however, may be variovsly distributed throughout time. AlthoughEquation 4 is su:ficient to describe the sound field due to change iqgas flow over a finite time, it ia insvfficient for application to proS-lems involving abrupt initiation or cessation of gas flows.

Consider a point source of spherical discharge area, At. Ifthe source abruptly starts and continues discharging gas at a steadyrate. a sawtooth sound pulse will emanate from the source (seesketch).

133

P -iK'

Pt;

P-

Ut

'Xo r x

Steady flow conditiona will be establitshed behind the sound pulse,where gas flow rate wil be

Atptut = Apu (5)

where

At = source gas discharge area, 4nb2:

Pt = gas discharge density;ut = gas discharge flow v.elocity;

A. P3 u = area. denaity, and flow velocity at some diatance from thesource.

134

If, at the source, the discharge conditioas are supersonic, i. e. ,flow velocity is equal to local sonic velocity, tien in the rangeb :. x ! xo,

= ((6)

and

u ( = 2Y (7

From Equations 5, 6. and 7,

2YP A t V4•- = (+

and

U = ___(•Y+ ! 19)

where

Pt = absolute pressure of gas at discharge;

at = discharge sonic velocity;

x = distance from center of uource;

P,a = absolute pressure and sonic velocity at some distance, x,frorri source.

At distance xo from the source, the gas will have fully expandedto atmospheric pressure. At this location, x = a

P P. (10)0

From Equation 8,'- \y + 1

At tA (Pt) +4/

135

and from Equation 9.

o -o (1 2)

where

uo = xlow velocity at pt xo.

P = ambient air pressure.0

Beyond the distance Xo, the gas remains at constant density and

atmospheric pressure. Thus, for xo ! x,

P P: 0

and

=pt( P (14)

and, from Equation 5,

lategrating Equation 15 for the boundar'y conditions of x =xo at

x 0•1113 V + 3y-1

t ru (P) o 4YXX 0 3 u: + I At Pt 3V 4 \ 7 t+ 1 (6

I. o"- 0 FO I ,T-tand t(o

U - 0 ~ (17)3uY t + I

which describes the location and velocity of a given discharge gas

pe.rticle with time. Consiier now an a*oruptly initiated gas flow

136

bwu

and the air particles immediately In front of the advancing gas front.The air velocity and location can Le described by Equatiois 16 and 17.The pressure of the air is related to its velocity. Thus. if it is aasurned

that the air ac.quired its ve!ocity by virtue of a pas ning &hock. 2 9 thenthe ov•rpresgure will be given by

++ F __. __ -I+"-m

where

M = u/ao, air flow Mach No.

AP = static gauge predsure.

For M ý1 the overpressure rrnay be esti'.nted by

Y+ Ip Y ----- Y(19)

If It is oassumed that the ar in front of the A1vaneing gas front acquiredIts veoýl ity through ilsentropic wave cormpression. th,'n the over-preseura can be expressed by

ZV

A P I + M] 2 11 (20)

F .r M e 1, this overpressure may Le estimated hy

&~P *1 VP 0 MI (ZI1)

Whichever case is assurned, shock or isentropic wave compressionithe ^ctual case will be torneplace between the two), it is evidenttoiat a reasonable overall representation of the overpressure interms of velocity is obtainable with

kZAP klM (22)

wher"'

ka and k, appropriate constants,

137

Now, a spherical pressure wave diverging from its scurce can bedescribed by

p = X(23)

r

where

Lp = overpressure at given distance x fro-n center of source;

p = overpressure (or sound pressure) at distance r.

Substituting Equations 16, 17, and 21 into Equation 23, the far fieldsound pressure due to abrupt initiation of gas flow becomes

YPOxOu 0

P = a. a 0 Pn (24)

r [ 1 [ -+ 1]1/3

Equation 24 describes a family of curves depending o0n magnitude of(uo/xo) (see sketch below).

(P/Pto)

iWoV

/PM "const.

..

ltT2 TI

It can be seen that in each case the sound pressure decreasesexponentially with time. The rate of decrease, however, depends onthe characteristic flow pararneters -)f the source. Except at the timewhen thoe sound pressure is very near pm, the factor 3uot/x ,is

138

substantiAlly larger than !, and the sound pvcssure can t,. estimated by

Pm(3

Taking the time t as the representative time period of the soundpulse and rearranging Equation 25,

x• )3 "Nf-

( •p,, "--At Pt

o 4_ (26)

Z! the time period is established at a constant pressure ratio(pm/p).then it will depend only on the source discharge area, discharge pres-sure, and discharge velocity, and can be expressed. generally, as

3V 1)

T fiC •TUt

where

C = an arbitrary constant.

This equation is so.en to be aimilar ir frrmr~the "Strouhal" frequencyexcept for the additional (actor (Pt/P,3 v . It is to be noted thatthe sound pulae duration remains relatively independent of the equationused for relatir.& the air pressare to its velocity. The only prerequisiteis that it is of the form described by Equation ZZ.

Some insight into the above problem is to oe gained by con-sidering the nonlinear propagation of stronag sound pulsefl. 13 Con-sider a relatively strong sawtooth soand pulse (shown in the followingsketch).

139

...

dp

By virtu- of higher pressure, the shock front (point 1) will progagntefaster than the pulse tail (point 2). The velocity of the shock front

C,= ao [I + y+ IPm (28)

The pulse tail. of course, proragates at approximately ambient sonicvelocity, ao. Due to this velocity differential, the pulse wiIl tend tostretch out %ith time (and travel). Change in the pulse time durationcan be represented in differential forrm by

dT _- •I P r (•

4Y Poao

Corresponiing to this increase in pulse time duration, the peak soundprc-2sure %.-all decrease. For the spherically expanding wave frontthe relationship betweer., pulse pressure, duratign, and travel can berepresented by

Tpmr Tlpmirl (30)

140.

A I 4i - -

where

T and p., = pulse duration and pressure at some referencelocation, rl;

T and p. = pulse duration and pressure at some location, r.

Solution of Equations 29 and 30 indicates that the instantaneous p*-aksournd pressure of a sawtooth pulse can be represcnted ir. terms ofIt* travel by

Pmirl

Pm = -/- (31)

1r-+ 1 P lrj In (!-) + 1 1I2YZ PoaoTj rn + I

The sound pulse timrie duration, as a function of travel, is

ZY PoaT I rI

Thuo, it is seen that the relative time duration of a soundpulse with long wave length and small arnplitbde changes littlewith distance from its source. On the other hand, short soundpulses, especially those of high am-plitude, can significantly incrasein time duration. This time increase is zccomlpanied by a proportionatedecrease in amplitude beyond that of the simple spherical expansion.

Conoider nov a long pressurized cylinder (sketch follow.ng)contaimng a gas. Initially, the gas is at some absolute pressure,Pl. and absolute temperature. TI. Initial velocity of gas is zero.As the cylinder is sudde.aly uncorked, a sawtooth sound pulse emanatesfrom the mcuth of the cylinder while a rarefaction wave travelb in-ward. Until the rarefaction wave reflects from the bottom of thecylinder, the discharge conditions at the tube exit remain relativelyconstant and dependent on the initial gas conditions.

If the initial sound pulse due to abrupt initiation of gas flow is repre-sented by a right triangle of amplitude, irrand time duration, T, then

PinT

141

- J ---

• Ut

XOr x

and, from Equation 4, the peak sowid pressure becomes

Po C I/V- 0 (34P

where At, Pt, and u. are, respectively, discharge area (Ttdz/4), pres-sure, and velocity.

Gas discharge from the cylinder depends on the initial gas conditions. 2 29

if~ Fj! P4,( "Y42 y .1*3. 6P.,

Pt Po (35)

L PolZ• . ,)- , (36)

142

a.d subsonic conditions prevail at the tube exit, i. e. , locaUy, fL.owvelocity is smaller than sonic velocity. +1 Zy/Y-l)

If the inlti-xl gas pressure is PI 1 P. (Y

Pt Z Pl(L - (37)

Zal 2aa (T (38)u -- V l------- ) O~ ; -+, -f.iV -

I

In this case the gas is discharged at a velocity j,tst equal to its localsonic velocity. This ic the usual case found in unsilenced (and mostsilenced) weapons, as here the pressures encountered are generallyabove critical. From Equation 27 the time duration of the sound pulsedue to uncorking of a pressurized cylinder is

3Y- I

T = k 2391

'at

where

d diameter ot the cylinder;

k 3, an empirical constant.

Combining Equations 34, 37, 38, an 39, the peak sound pressure dueto an uncorked cylinder becomes

Y + 15-3Y

m ( (T"•P )• T(40)

and it seen that the peak sound pressure is directly proportional to theinitial absolute gas ternperature and only weakly dependent on theinitial gas pressure, as long as it is above critical. However. sincein the gun.high pressure is generally accompanied by high temperature,the peak sound pressure is not completely independent of the initial

143

cylinder pressure. If it is assumed that the gas being dischargedwas compresse:d isentropically to its initial condition, thenTI = To (Pl/P,,)(Y-l)/ ', and Eq'ution 40 can express the peak

sound pressure in terrn.i of qniy the initial cylinder pressure. Theresult is that Pmrn On p1 .f+/4Y This seems to correlate reason-ably well with experimental data available to date.

The sound pressturt field of the uncorked pressurized cylinder

is directional, pressure being higher toward the front and lower rear-

ward. Directly to the side. it is approximately a representativeaverage. This direttionai effect can be approximately represented by

Ping Pm (41)

where

Prng = peak sound pressure, given axi-muth angle. 0;

Mt = ut/aotdischarge Mat ,.;

n = constant equal to ap >..imately 2;

Pm = peak sound pressure directly to the side.

And the peak sound pressure level at given azimuth angle, of course,

becomes

Lmo 20 log PO (t2)

144

APPENDIX D

GUN SILENCERS

ConRidcer a typical silenced weapon, consisting of a gun barrelof volu•.ne v and a baffled silencer of volume v7 (see sketch below).During Its cycle, the projectile is accelerated by the high pressuregases in the barrel. Following this, the projectile travels throughthe silencor while the propellent gas expands into the silencer cavitybehind the. projectile. Just p-ior to exiting from the gun barrel, the

propeUent gases are t-pically in the vicinity of 2000 Fand 3000 psi.

V 1 //v

i L

INI

During its expansion into the silencer cavity, the propellent

gas mixes with the air contained within the silencer. The air,originally at ambient prersure and temperature, is compressedwhile the propellent gas pressure and temperature naturally de-crease. In a typical silenced system, with the silencer volumeof the order of 20 times that of its gun barrel, the conditionswithin the silencer just prior to projectile exit are of the orderof 60 psi and 300* F. The projectile, being subsonic (presumably),travels through the silencer at a velocity close to 1000 fps. Ju-t

145

how quickly the gas bdidind the projectile expands into the silencercavity can be gathered from the following graph which shows theshock, sonic, and flow velocities of air or gas similar to air, asa function of presatsre.

tea~~~ ~~C a- "[V.. * -Z-' .-- i.7--

--- ' I-, -_4 4F.,ý--.l

~~~~~~~- ,Ut -i . -,- -i 1 2,.• .. .. .

22

/I ID 20t]~ ik- int V0 2•

Froin the graph it is found axot unreasonable to assume that, in atypical silencer, the gas pressure is very ncarly uniform ilongIts length at the time the projectile exits the silencer.* Consideringthe propellent gas and air undergo isentropic expanaion and compression,respectively, tht absolute pressure in the silencer at the time of

MOther assumptions may be necessary in the cnese of a supersonicprojectile.

146

projectile exit will be A•l \V/y v2

" vz

LVi

which can be simplified to

PI•j y

VI.vI

where

P = absolute propellent gas pressure in gun barrel at theI time of projectile exit from gun barrel.

P ambient air pressure (14.7 psi);0

v= silencer volume;

v= gun barrel volume,

y = ratio of specific heats for air and propellent gas (actuallyfor air, y = 1.4; ior propellent gas, y o 1. Z).

Similarly, the absolute temperature of propellent gas in the silencerat the time of projectile exit is

/Pl(Y - 1)

T = (3)ST

1 [ / V 9\ 1 / Y1••,

where

TI abuolute ternperature of propeiient gas at the time ofprojectile exit from the gun barrel.

147

NO

The abAsolute temperature of air compressed in the silencer is(pu/p o )Y-I) )y

T (v2/•l . , which is very nearly equa to TZ. Thus. the

air temperature may be assumed to be the same as that of propellentgas (i.e., that given by Equation 3).

Projectile exit from the silencer will be followed by an effluxof gases. Ifj Vthe time of this exit, the silencer presoure isPzgPo )Y+ MY- 1) •1.9 Po, then

Pt = Po (4)

and

where Pt = absolute discharge pressure;

Ut = discharge velocity;

az = sonAc velocity within silencer at time of projectile exit;

a 0 ambient sonic velocity.

To= absolute ambient temperature.

In this case the discharge conditions will be subsonic; that is, gasflow velocity will be lower than sonic a. the point of discharge (ut% at). If. on the other hand the silencer pressure at the time ofS P2 YP I._ .•- y/(y-lI) . Pprojectile exit is p2 k p0 +

then

Pt Y+ (6)

and

u 2 a2 t Z a (7)

S4 o

148

Now the diaci-,rge conditions will be supersonic, with the flow velocityat discharge being equal to the local sonic velocity (ut = at). Thic,in fact, is the typical .;ondition to be expected in most conventionalsilencers. As the projectile exits from the silencer, the abrupt un-corking of ir."ernal pressure will generate a sawtooth sound pulse.The time duration of this pulse is given by Equation 39 of AppendixC, - . !

Tz kd\P (8)Ut

where

k ow 3, an empirical constant;

d = silencer exit diameter,

The peak sound pressure of the sound pulse is described by Equation23 of Appendix C,

Po Pt /l (/yPm= ZirT Atut

where

P0 = ambient air density;

r = distance from the weapon;

At = rd 2 /4. silencer discharge area.

Combination of Equations 6, 7, 8, and 9 yielda the peak soundpressure cf an abruptly uncorked silencer, to the side of the wea-pon. as

Pm Y + I (L25 - 3y/2: (7 T7 ý- YlO)(7f7-l 4ydTZ (10)

1) 8Bkr P

where

P 2 and TZ are the absolute silencer pressui'e and temperature,res,>ectively, established b.y Equations 2 and 3

1149

If the silencer emperature is related to the silencer pr-..ssure byT7 T (P2 )(Y1•-Y.i ,which is not an unreasonable estimate, then

Pm X P z +I)/4". The peak sound pressure level of the uncoskedsilencer (front Equation 10) can be described as

y 84yY J

It as ntncrc¢ting to note the effect of heat Absor'ption in the silencerOn the Feak soi~n4 p•'etsure. If, similarly to the above, the salenccr'spressure is related to its terr'perature by P 2 • P 0 (T 2 /To}(Y'I /y, then

tr le expressed as a f Tzion of only the si-le~•; eep~atuewhih ives P~n oc't T•{~l/( . With maximum

neaIt absorption in the silencer, temperature TZ will have been reducedto ambient temperaturr To. From Equation 10. the attenuation of pek

sound pressure level thus to be attained in a typical silencer is in thevicinity of 6 db.

A certain umount of blow-by in a silenced system is unavoidable.Since, for the sake of syoterr accuracy, a clearance must exist beetweinthe silencer and projectile, some propellent gas usually bypasses theprojectile in the silencer. The effect of this blow-by on gas dischargefrom the silencer irrucediatvly after projectile exit can be surwnifedfrom the following.

The gas discharge following projectile exit from the silencer isprimarily dependent on the quantity of gas contained in the systcm atthat time. which, in turn, is determineo by the percentage of gas lostthruugh blow-by. The percentage of gas lost can ie represented by

-t(Ar) 10 (Atotut) dt

m p9 (vI + v2 )

where Am = gas mass last through slow-by during timhe projectiletravcrses silencer;

m = initial total in?-ss of gas in system:t = time ;P2 - gas density in system at Um.rne projectile exits silencer.

The duration of blow-by is limited to the time it takes the projectileto traverse tlhe silencer. If. during this time. a constant and unre-stricted (maxirnurm) gas flow raie is assuxned, then

I50

S. . . . .. - I l I I

Pt(~ At Ptut)dt =At~tutt (13)

where

At =ilencer discharge area;

Pt = discharge gas density;

ut = discharge gas velocity;

t = time it takes projectile to traverse silencer,

With maximum diecharge conditions,

Pt \(14)

The silencer discharge area is approL.rnately

At O I (16)

where

vi = volume of gun barrel;

= ler.gth of gut. barrel;

The time it takes the projectile to traverse the silencers ia

t (2aoM

where

2 =silencer length;

M 2 projectile Mach No.

With these definitions, Equation IZ reduces toY+l

V+1

151

within tetrersrit h ainn ecnaeo a yia

effect o i the gas dinchorg, occuik r'ng sit th.w t~:re the' pruiectiie eyxits

from the silencer.

Examination of F.-juation r,!veal-i tha, th-.z pekk souund presasureis invereely proportion~al to iu time( durt.tion of a give~n ;~oind pullse.In a systern wntwre gas discharpe is initiate'd slowly, the s-?und pulsetime duration O'z govtorned by ltec tir.o it taikes the sybtemn c: reach agiven dlisthrg rate rather than by -a s'term's maximitm dischargeratce (Equ~ation 3). Fhos, it becuniii evident :hat the.i longer thet-yettm takes To r.*acii its maximirno. Lgat d Iihage rate. the. quieterit %%ill be. Practically, it nivans tka~t it ;:, dc-Lirabl.* to start the gasdischarge froiss the hiit'ncer slow'-y and e~arly in the process, graduallyiitcreasing the ditxcharg.! tu whý'n the projectile exits from Lthe silencer.If it is as3umed that the gas discharg-. from the silencer can be initiatedat the. time pro 'i~clil.: e*xits the gun b~a-rrJ, the tinie restraint is im-pobcd by tlwe silen~cer length and projectile velocity. fh titne inw~hich the ciisch'at ge can inc reas,Ž fromn zero to maximurn will be

T ~(9aom

Witt, [his timc jh--;( lasnd FpIRatinti% 6 A&nd 7ý, Equation '9 gives the

pc.3l'~~~~~ 4. e r-uea

Thizi relat;inship gziveE- thco -rriv.iroum pra%. sound pressure of a sybtemwhi~ga3 OircCx '. icc. V~i initi~a:-d graduauly, rather than abruptly.

Compiirisoxi of this -tiuation %#i th LqýLatioii 10 and substitution of typ-icj. system qua rktitat!s revv~il that attenuatioris of as much as 15 dbare rnbtainabl.ý with Elie co i-1QU dA .ar. technique.

Attenuatioti of a pI-&-7Jrsor waee in the silecaer is somewhatdiffurent from tb~at c," a :.dast wave. Wlhervas th-( latter involves highpr,-.sar~t; which! pr,.-sent a iorictn' . ass trans fer problem.the former can bi, xnocttd tf- rxpandt- ,ruvagh the silencer at almost

5i ''

ambient sonic velocity, This ullown the asiiumption that the re-flections of the precursor within a properly designed kilencer willhave practically no effect on the forward wave front. In a properlydesigned silencer, the baffles or other silencer components wi•uldbe such as would not impede the natural spherical expansion Ocf thewave front within the silencer. Example of this can be sees. withthe rearward-slanted, coaical baff'es.

Consider now two gun barrels identical ia all respects exceptthat one is equipped with a sileLcer (see uketch below).

P3 V-3Km¼u

r r

-- .- '

In the first case the precurbor wave generated in the gun barrel willbe unattenuated. At some distance r. in the far field. itf soundpressure will be

P; pZ £ZP ---- (21)3 r

where

It2 = silencer lengtL;

pZ = precursor sound pressure(gauge)at distance f from gun muzzle.

153

-4;

In the second came. the precursor wave will first expand unimpeded(±.phericallv) in the silence3- prior to expansion into the atmosphere.At the front end of the silencer, the precursor wave front wiiI geieratean abiolute pressure, which can be eatirrated by

Pz O Po + 2Z. (2 2

This pressure will induce a ilyw of air through the silencer muzzle.The velocity of this flow will be given by

Expansion of this equat.an and elimination of lower order terms re-duces the flow velocity to

ut W Y :- :• ! _ao. P? (?41YP 0

Corr prnding to this flow velocity, the dischre. - pressure(guage) at the silencer exit will be

Pt 4 -i - VI•T-I}p?0 (25)

Spheric&l expansion of this overpressure to the far field representsthe attenuated precursor sound pressure, which can be written as

P3f o m d -- pzd (26)4r 4r

where

d = diameter of silencer muzzle opening.

Combininp, Equations 21 and 26 gives the attenuated precursorsound pressure in terms of the unattenuated quantity

932 2%Q e 7)P".! V Y- Lt

154

2¶

-

The attenuation of the precur-eor~in decibelSis

S= 20 log ?_ V/ (28)

Substitution of typical quantities in Equation 28 indicates that aproperly designed silencer, approximately 6 in. long and . 35 caliber,can be expected to attenuate the precursor by some 30 db.

An interevting problem presents itself in considering attenuationof the silencer type shown in the tirst diagram of the foUowving sketch.

Here. the silencing volume in separated into two chambers, one in,front of and one surrounding the gun barrel. A bleed hole (or seriesof bleed holes) leading to the surrounding chamber is provided inthe gun barrel. As the projectile passes the bleed hole. the propel-lent gases in the gun barrel expand into the surrovnding chamber.When the projectilt exits into the front silencer section, the pressurein the gun barrel decreases and the gas flow in the bleed hole re-verses. Yf the bleed hole is sufficiently small.then, because of thegreater initial pressure differential, gas flow will be faster into the.surroundyng chamber than out of it. This technique is capable ofsubstantially reducing the pressure in the front silencer at the timecf projectile exit. An optimum exploitation of this techniq ie wouldbe to introduce a one-way valve in the bleed hole leading to th-surrounding silencer cavity. Consider the silencer with a relativelylarge bleed hole, so that gas flow into and out of the surroundingchamber is relatively rapid. The gas expansion processes will bevery nearly isentropic so that the silencer pressure at the time ofprojectile exit frormi the silencer (from Equation 2) will be

Pv2 + P v3) +I (Z9)

155

i 1,1llflll~ lliW~ lllLl

where

P 0 ambient air pressure;0

F1 pressure in gun barrel just before bleed-off;

v = volume of gun barrel before bleed-off;1

v2 = volume of silencer chamber surrowuding gun barrel;

v 3 = volume of front silencer chamber.

In a silencer with a bleed hole valve, the expansion process up tothe projectile exit from the gun barrel will be similar to that above.Beyond this point, however, the gases remaining in the gun barrelwill expand into theforward silencer section while the gases in thesurrounding chamber will be trapped pending possible slow release.Isentropic expansion up to the gun barrel muzzle gives the gaspressure as

; F/_ Y

~p +1 (30)

Expansion of the gases remaining in the gun barrel into the furwardsilencer secticon gives the silencer pressure as

P3" 0 (31)

This, combined with Equation 30, gives the silencer pressure attir.ae of projectile exit as

"P 1/y v Y

;0 ) - -+v (32)P3" Po v z v 3 +{

Solving for minimum P 3 ", it is found that the greatest reduction inpressure occurs when

156

r/Y

Substit'ition of typical quantities found in silencers into Equation 33indicates that in order to obtain maximum attenuation, the surroundingsilencer chamber should be approxhately 0. 7 times that of the for-ward chamber. The difference in attenuatitn of the silencer with ableed hole valve and the simple volumetric silencer can be estimatt d*from

A•L st ZO log 13 ( )4 34)

where W• & P3 " are as defined by Equations 29 and 32. In a silenced

system with gun barrel pressure of 2500 psi and silencer-to-gunbarrel volume ratio of 20, the bleed hole valve technique yields approx-imately an additional 4 db attenuation in peak SPLI. The technique canbe expected to be more effective with small volume silencers and lesseffective with larger ones.

See Equations 10 and 11,

157

APPENDIX E

SILENCER TECHNIQUES & REPRESENTATIVE PATENTS

The following silencer photographs and patents are presented ac

reflecting the various silencing techniques and con'cepts.

The photographs (pgs 159 through 163) of sectioned WW 1I German

experimental silencers show sorne outstanding silencing techrnques,such as flexible baffles, vortex-induci-ig channels and rearward slantedsteel baffles. Also shown are quick attaching silencer clamps.

U.S. Patent No. 6£8,934, issued Z October 1900 to Reade MaconWashington and Alfred Willis Capy, "Attachment for Barrels of

Firearrnh. "

Austrian Patent No. 5478, issued 1 June 1901 to Josef Hutfiess, "Devicefor Silencing a Firearm. " (Translation)

U.S. Patent No. 958,935, issued 24 May 1910 to Hiram Percy Maxim,"Silent Firearm."

U.S. Patent No. 1,000,702, issued 15 August 1911 to Eugene Thurler,"Device for the Suppression of the Report of Firearms. "

German Patent No. 629,404, issued 13 March 1933 to Aans Eirsfeldt,"Silencers for Hand Weapons. " (Translation)

U.S. PatentNo. 2,448, 382, issued 31 August 1948 to Warren P. Mason,"•Silencer.

U.S. Patent No. 3,138,991, issued 30 June 1964 to Richard L. Malter,"Firearm Muzzle Attachment and Projectile with Expansible, De-

tachable flusk."

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UNITED STATES PATENT OFF~ICE.

JI.:ADF ?JAr;ON WVAslI.XTO'N AND) ALI'RVD WILLIS CAPY, OF DALLAS,TEXAS. ASSI&W1011S OF ON1 -VOVRTI1 TO SAID WASUINGTON.

ATTACHMENT FOR BARRELS OF FOREARMS.

8wXCMa&=fl forwituit pars of Latteors ?staer No, 6M.O4 ,dateid Qescolor S 9M 00

Ta all whom ig mo,.y roinroen: *the barrel bysastrap or its squivaleut. InBe it known tiott we. 1tV~A1B ZIAA.OW WASHl- order t hat, the extension I1I of :.b.o body and

iwroand Ai-itt~oWtLLISCAPV, Of I)Allan, it) fart IbI" chainber lIn the body lwopopr wayIII the County Of L)KIlIA- And Scale~ of To%"., be read:ly clesnod when desired. the tfearend SS

S aeit.eeanwcolunttAtrmn portion of the extenuion I I iscivoow by a plugto the Karrol~tof rirearmsN. of which the fol- It, screwed therein or otherwitto detacehablylowing: I,. a (.til. clotr, and e*cit, dtlnsciption. securel in plsc3. The opper surfaw" of ttte

Oue object of nat) Invenition isto powedea catinal A is slush with the varrmpoodingeur-simuple, light, yet d.trabie icviric adapted f., fact, of the 11snere In older that the eight Cf 60

.s at tach eu~ut to I tho in urzzsof ri flea, tousketa, tsid barrel ftbail not. be Intorfered withb. 'rheand otherarn~epa~iapt-ed to lirebulle sand to space within the casing A and the extenstionso contstruct the atm~v-lament i1'st it will we. I I may bo Iteroed an - expansion -chow ber;"teri~lly tatodify or eoitir'lt prevent the now*a boot certain portionto of ibis expwiRi~oncbaw-Inside when it wspwo 6t tiuvchitrged, and w~ill ber are sbut off, As will be hereanaftarsttaled. 4s

5 ssa~rt ISri sUlptcax%the d iOk alcimt entirely ITb. 'iody-easing A Is eadpted to receiro awhen Ilsck powder IA usc; cap 8, the cap bel a# at o;he forw., -Q or dellIyv

A fuirther.-hjec'tofth tIinvention oo io aot- eryeod oft he easing.oW this Cap '--Adaptedfain the ratio abov'e pet forth without imtpair. Itoolide within tbe body-eataingand i held 1,ioe~ the power or ai-eurocy of the weapon. engsoatewen tharewitho in any approied man- ?o

o The invention e ,o%istg itU the DovOl Coa- ocr-asW, (fo elAMPIe, thrVIagh the mc~ltIM Ofotructioa and coabloinjou of the omovera) spring chlyjor gn"Itato3--as rhown In F~igs.pArIK, "s will be hereiinafter fully aet forth. I &ad i. The Inner !Ace It of the eap hise

sell j-lantest out in the cloinini. Inclined. the itClid~ioarl being (rona the up-Urfefrvnree1 to Ito hsw to theaowteomi-mylar per edge downwardlyotnd forwardly. sud the 75

S .)rawia.i, foroanunga part of lbi'tewviftcatioa, inrcer-faceof tbocapia open frontapoor;atoirin wbih~ct~imilotreharcterooof rrfertenc. `idi- nrit oom os terhtp.Th.CAte c-trer -skintdlng pccrt- ii IAli the fleurta. copper poirtion (if the lisanr inclined face of

F-iguire I is at aside dclevAt io of a rifle end thse rcap 1; is provided with a defllctiza-plateMe. atlachina-al applitO kheertra. Fig. 2 in a 15. ^nJ the maid defleciinoor-plate ha fin open- so

.olongitutidngal acotmain tiarumagli tb,,ettachment, ino: 16. the crnter of oisad aoenlng bjeing inalm-wn on a larj'er dcale than in Fig. 1, and lonritu.Jiuml Alinemeent with the axls of thealao a longitudiunal socgion through abhot pnr. bonre A' of the barrel.lion of tbe baurrel to which the attacbtnent ao Immnediately forward of the opooltog 16 inApplieds, a-ina File. 3 1!1 0 'rauftrerwe vertical the deflecting-plate, and at the forward np- 13

S eei'tion taken prictically on the lint 3 5 ot per end smf the cap a chamnber 16, is formedri-g. 2. pro)ti led with Aninlet,17. theesoconrof which

.4relpreeenlaacaaina,wl. chisuauiuatlymade inlet is ina plane with thenconte, of the axi*oval in croas-otecti'in. as shown Ito Fig. 3. of ih3 openinR 16 in the defolectinug-plate andThis coasing: io provo d-, v. itb I. eollAr 10at the tbo axi- of the bore A' of the barrel. This go

0 rtarec,4d Of I!& hotly pOltiOll, an~d the0 said ccl. alinemenot Of thl OopenIngs 17 an0d 16 witb the1ar Is aoiaptetl to be vcres'nd umt.si or other- borp of the boarrl to In Order that the bulletwieo attached to the forieord or inuoule end d.scharo'xi f(mm thoo harrol way pwo 4hrinugituf tho barrel A' of a guin, cas shown particu- the- said openingto 16 snd 17 and on; tbirnjrhlarly in Vtc 2. At zhe orena- lowee~ lorttou of lth. rhanciber £6' withoot interfering In the 95

5 Mei twsay-caWnqoa A it tubular xtteustoa 11 to fligh*.e't f'f-rtre With Any Of the meschanbimfortned, which 1s %mis..siYty ircular In Cracks- designed to s-sline the X6ases.

sevitlu. but wasy bat.. uthe.- Ioaectoa The Inner face or wall of the chamber 161cmatour. rho venioniei I I fiora the c-imait to ioclhed , And a flange 18 to formed opcoIs adaopted4 in ext. ,W roarweoilty IOwneAth Cho thisk wall aroondr lbe inlet opening 17. The Noe

or brrvP a nccc-wary dIut~eanter when the ca-ii' flugoe In is &d~pted as a seast for a walrt 19,is attached to tho 5arrel *and - faciteooed Io which valve coigeas Xhe nlot" t7 of the chazi-

164

VNI

b"rfIWmuwtvllAt~lYifto-rI thdix-eharge ort llI.f n.mter 1wrtiamm tof the lIepoustit -will be foundbullet; but slotru~mily ilavtlvme ~rI'm I- miao t.. hear 1410.14 1s~ siw m V s ill fiarsly A dsir~tw lino amtid"a*Ussi. 1"On inner.. (nee of th*- lomwer jrin .s thon cxiin .4o tlan lsimu of tho $un.of the dui'.Is~pmu.15. ^4ftislint at p..mi- liatv.ug Shim-s iS..craitX (jur in.,-nuoto,* wo

S tions pairtllo-I with tho isaic of tile. 'n;rr fmacs ;Iinais,. new utmad dftcirelmit soeqro by Lei ternof the cap It, "a shown ill poiitl %tlese in ~tmFig. 2. The npesin~r 16 !'A the" dl.fiucuiii. 1. A vaw'sscarrnmnorr,) ftor alau-hmmopot to thepliltit 'smt MII- i JI 10101ro-1,. eftpf, mnd ir, ordemr hmirrorl of at atiga. annd h.tviqae nn anottIt foriti j;thsit tile dimwblam-ge oit thin bulle mht 'X0 nut it" ~,mltin inclined defl~eoetins!- plitie mn ,gtid

Ito ltngw"l is c4-rtwvfmoumI' g~ up'nmi 20v i.. mamle I ca-mina andl A VAtIV norwokUy fir41 in an ott'ain' $hhu sbgmer m.id1 it thin vaslve. oaid when htim Ip.ition And opervotted by LI'. Ia&ee 10 eltee.~v~v L hi~ b-nviiig Muin~5t lime 4tfhm4.~ lb fme.t.w ;ipe tbissoill ifter "idm bullet lima.plate 13 t!%m opedviota in the valve and the omu.Iwhl (rum Ia~su~uaumuta~md-Sopermilsa Hi the etige o! ilit deflectin-lk.malm scrilieud.

IS re-goiter. Awl.-. m.tv al ajem, s tp-niut' nufficien.r also ? A i-e'dnipr-'ti Iswiwtb taa-e-onder.asngglu Uaisttrr4mi~dpooh-Ageof ithe Atn-ssIw. a-mvl diamsrtmzv fur Conhitetion wit~h

bit 10Ldie, ItArrisI of #L activ. b.ý lasid ellioimber krAvialogAn atrm 21 iN "wutred to the front facto nt nit .tvtWa fur a 4ioml~e?. she ,iAl i-vm~ina htiovinc Ss

the lower riaoi-mmm 4~ &he -a. 110. As arm be- so tmbui~u.r totti"mibl..ai t.,imoun,: peit of le PRO-to isia A& ri-ght A")a-. to tha outer face tof 04Am1 lotidlook1iiiig -hamsbiti~sr and eitoakmsndg sainti

Taltro, and the %4vo'a ins pmuvolosi is, iie %,ap U ivaoliv, bt-rnatik the biAa-tel of die gun. a dlo-by a in It~' thatbis is pause~d tkiroiighthe Ii"-~ v-slo. lor Ato rrar food ut mid tubuLar eaten-aud Ihsouxh Ali# said aria. at%-how .lmwin Fa igs. nimos n. Va~ vleoporookko by thie gaas.l to tkw*t goI at&~3 The. valve Ito in imcd it. it% oroa ne- tIli* im&ilt for the us iwtntafirrsuitd hvlta hletb

25 altion-tbat ii, iv PLtageosmaet With the d.- 4shCAPWd anmd a auppart, niag t, whir') -.Aidfietelngpla.'--'y enasmti nit( a supring 23. vctbt norwatahi rtemK ilia -aid ioppor: beosulf

nusmsallratitat-bo~d to :h#- bottata oitter wall of immcoted iotstwri e-ofbgs.ta .an'dtheChenaille 10.. &he 141o-int! liatt Ing Lvmoiing the oustlet for the bulle%4.itrt'tal ga sAaliusst tLbs uplioeesurface of ;he aria 2 1, an mcrit Ai.

30 ahowe ina Fig. ;.. lnont.-riimal thevptrinr2 3. v.Laing adaptad for atiamo-hse~nt Sol thewety loto rvt tein orma,-vml tinhi-es nervnmear) * bxrr.-. if ngun, a cbmsmb~w-r at the forvt~ol aod

Ant openlug is snail.. in t:io fsmsist of Ile, enap of %.Ai- ceA.'iS mand bjkv~n: an' lah-1 in diini-1*6101w 111e 471mmImmior It;*. A1141 thilt Uptiing is nor or tcr wAll in' itu with Lhte borv gu t" L i,y m0otvi&l7y .-lmmWm.-. by It lmiutek 21. gun. a lato to vAid cmuing bie-twmr".e the M-ar

3S Ito the filwraviamo of he itltaonhmei shon a. ondi of *sid elvamniwr sand the enod of Ib6 vl'a-gnlu isi fined im'ImwSs^ blem in-whargod Ame usutal. barret i..4d a pmivoted va',~ u'wrivaily wy-tii~gand titliosa.Aeme nomt twoisi tIm.. barreli doia., Diet min' the vaui plate, the pAin act] vmal'i topcng10ouch or iestorfr.q. with I* to- muet'balnm of the eunA~t rot-led to permit, of the pmswage of t iled- itts

StLachusent. am Iet" hervisfmoum" been %mtnitoo. I let. the Paid -m botifiz adaiploe to orkls, tue4o The eiksdinurt-oea strike the delkfvtinsg. o mp'ssuig in the rear et-st of it.id ellaot"-wr 1Wm

p~Jl.itt 15ssi-I thes v.as-s 19 at the 'awe miummtottt. tuediale~y afivor the .mcape of the llu.'L!-. bil-41The drd-flsrtimmg. plate beiatriocim Sind inclisned ismg rarrctedm to slaid cl.-niug pruntion hy #be Akv-

towanri the v~Iive tiarms lhtk flos tit Aia-n 4miwoo- tiillf Of tjokW .Ij5, IiiAut!Ally Ma dorokegitwd. isoWardt In dmrwelion of Ithe Valv~e.aied tho Vavjtc. 4 A dm% ive xeselape to utcietiol thi' nti:e of

45being~ free '1muvto outwardm is thrown agitilmait the vatilwoioll nf a t. ar oan zs'm vrtint the -Ito @#*I IA, ma boam mii dgsfed liuss in File.:. e* Ape uf aitoko Croon Ishe ieuAxlo o a gun, m-aidand ho bolds the,.. untinl the in~t-O preasmare of .Ie'%jLe. nuoM1j.*jAasOfacM CS~ZrrIastwMj (fr &I.-due gee in the ox;inqsiuss-ahbaber smmt barrel~ tacm hosm~et to ti. muzzle of a gun, the csaing siSof tho gmin bronmntineqnast othe -ugsesdo, mreim botinK txo p ided with a down* Ardl) soid ('i-

So sure of the Atnuottamers.. air plo.% the temIiou wardly exteudmng doadcetminx-plo, to haing'5 anof the W1 ~inn e3. vbetroulain the va~lve u-ain opinving @itine wa'.ith she &ill- ut the t'attim.olikkat aend this gun m-. resa bt~ mramajtbr'r ..i&.it. j lm..CAMIgbismgeit~~rovid"I wathem pkat,..a~e-vfyThe gAin. isuestex of rurbihm:ig inptu the air Av fur a 6.&diqt foturArd of the de flee~t to;--late. i toUSUal, is LurnsemI hy tle vmsIv,. 1.4eak law Ilb. -oi tua & alto s~omrtimily rv.,Ituseg with lits uppo-

55 etipatoflt-chatauber. abibub Lbmo gAo, ita-if h44 endi on .Aiad &n~eia-tl5 mit admipteds to*orlowd. Trbv actiosi ma set) sguim.-. tv is.Ytiri be' oummed to m-tuckw- -.sd ga i-wa) by theibs "s tpa desw&ritmosl (tilowooisc ~bc oimekr mu escvuoialagiciis u(giigia wsthim thedv"aidrsitg,prairua-lly A Iioaretone Cf tiuse. ab &44Ke Htuwd. 325

4e cubic conit Oita 401 tb* mitrdof st the Acun, ac-ts gissa. A s-a!-g %UAUIJV4s- Wa. the 11113111 Of said

aubtsanttuakly i"aL avirismmls.umsr &oil at Shem tisne. tar'-e,- *nmi A V.4j. ,efM0uiqUtV t -a-.) usll iltmof firing osto aokeiinvois~ilo. Upsmeia ructsmg fit-l 'A rd mInD4 to(f timt 04.-1U_ I th u-is V tmemmi prgo-opOINN thel ibt.e#h Of the tgmis $AS hkil A,$ pi-06t vided vmtith atu lumlism.-.' detftlie-jimn pto bia- t10Iiii- after fvins: -t bmullet &hu cxmoih~b its$ oi1 u otpem-m'x slim-rvit to ['it' with tho, axis

6S bor will Its lomtidi pmratitmcsI0y film-mi with a .4 1imm. l.,srr, V: u% vit.laosom Wr fmirward so[ the

light smooke; but tbu dorptmipi us-on the Lasittd I d otistg. plaitc, prostrjlm-d astbk -.s uolaismfltan'd geooves is ot)O more thaem Usiasal as tbo Also in Lu. withm the &.%i. of 0~-t bat of the

6 5

gun, and a valve having bearing ntormially Ai citi easin arranged fora*4aoebmntlt to th Sagainst the deffeating-plats, the maid valve barrel of a gun and provided with a guc-coa-being forcood to0 a seat rA the, iolat of time *aid denning chamber, anid a cap removablir se-chsmther, by the action of tOe gas atctaou- cured in tbe forward and of saiod easing and

5 la&ed in the barrel and back of the% Aald valve provided with a chamsber bawing an openingand deflentiog-plats, af for a hullet, has been is line with the axis of the core of the gun 6odisc~harged, a* dowr 3d. Miad fOrMing & PAGWO~ for A balil"t. a valVe

G. The t~oartalmtion with the barrel of a pilvoted Inejmid cap anO opprat#4 by the gate"gun~f a wugaleobd iohe ,ta4xlof said to close Lb. outlet for the bujllet Immediately

to barrel, a cap secured in the forward and of after tbe owcape of t"e bullet, the .Aid Capthe csasingand provided with an iuinotl ' dit- being provided with ani opening in Its frout 65flectintg-plate havinx as openinpg there'in in bvelow thessid chrimbor~and acensureforsaid

l10e with the axis of the barrel, % thamnbr all eniugt. aulhstantimll) "a dtitirihed.forwa~il of( the Aleffectioar-plate and provided 3 A dpirice adapted to cotntre tho noise of

IS With an imlet-Opieniog 311; io line With the thet rjrploaou of A c-harge stud preventL the es-valveemat and a mPlrlug-prowed alenor- said device comnprisingc Acasing A-arange-i fo0nuaily rmeting atgainsot the dflecting-plamauad attachment to the muzztle of asguat the caosinsiadapted to be forced sagame'et said valve-omet, being pr-ovided with A pnaotg-waV for a bal-

so sulostantialiy a" described. -let, a valve for closing maid passage-way, a7. The comablnatlon with tbe barrel of a spriesg for normnally holding arsid vAlve open., 75

gun, and a utoling Attached to thbe muzzle of and a deflectilog-plato for turainig the flow G,:W barrel and having a tubuolar extension at gas toward the valve. the valre being carried

the rear lower portiou provided with a renaov- to closing position Isv the guami.a5 able closure at Its mear end, of a cAp remov- 10. A casing fair attachnuens to Lbe muzz!.

Mby secnred In the forward ened of the casinge, of a gon, a cap removably sarcured in the for- Sotb. Inner fao said cap bring inclined from ward end of Paid naning and having a valve-the upper edge-downware~iy and forwardly arat with an opeaning fuar the papiange of theand theo aaid inner face being open from a ballet and a v*lve cartried by said oremoru~ble

So point at WnuearietsbtoLim to a oinit near the err pand free to swing. the said valve beingtup, an iuclioed i11iefetiang-plate at the upper nurainaly held In sit open poamiuon and adawt 95poertioin of the inclined intner fanse of the cap. ed to be moved by the a.eiion of the goaf toLb. raid glatis having &a opening is its loweq a clated posimion. s~abitainttally as deseebed.fdg* in longitudinal alinemnent with theaxie I11. tcasingasrrangeiforauaaehmeuto the

ss of ilb. bore of t he boarrel, a. chamber formed muzzle ofgit cin. aremovable cap fitted in theat the forward upper end of daid cap aud for- fo.-war-i end of the camiog and having % valve- gowardeofthe plate. the saidclaiplierbeirg pro- oea wishat; ope~amsg for the passAg of theTided with an Inlet in ita Inner wall in Ilin bullet. the axis #of maid opening coincidingwith t he opeonKn lie the plate A-d the b.;-aof with the axis of the bore -f the gun, a vaive

4* 0 te as,-el. the inner wall of Asid t-hambeir bu- cArriod by aid cap and free toaswing to closefag iiclitiedsand having afltacge formned w here- said openaingc a sprinic for wome'ali'- holding 95on rround i he Ilae. -opening sand coost~i~utissg aaie auglveIin Lb.open posiLkos,a anti defllect.-A v81lvcw11`a1. And a pivoted and hipringt-prees-d ing. ploolo carried by the cop and ar-ranged tovadte normnally renting at its i~pper end defleem . to games toward the r.asve, the said

45 Against the lower portit of the deflecting- Ivalve '.siumcloasd byt the ectionot cbs gase.,4plate anti having *a opening at its urper edge Iwhereby the -aid casing teceivessand clonfines isooforominig with th. opening is the lower edge ( or A time the guessf retnatlang from firing the.4 1 tbedeflectiag-plata.r peasageot-i the bul- gnu.let., the said valve beinig forced to 9its seaL at"3U~3W~l~i

So the inlet-openingi of said chamber by tbA%.u in.-AOI A11111Mqt144 of the gasles, Liter a bullet has been dial- £LNUS WILLIS CAPT.orhLrited. the froat, Of said cap Weow the chum- I Witesses:;)or having -an openinae pr~vided with a ro- 0. A. llpitkezvgase-ioable iclsure, for Ole pur'powe sot forth. 1 .. W. KILLT.

166

4.

a It. ishereby awrtilb that to Letters Paten No. 6W89S6, ganted October 2, low,.upom the appleatku of Reade MaaoM Washington ad Alfred Wills Cspy. e oDali.@1,Tems. fer an ifProvement in 11 "A ttadmm for Bearre of rFhem,." whro appearM- rquiring owrqeo, me folows: Li the e•rt and IL the pristad head of the specdISes

Ston, it It stated that they have saius -Aiu rth of their right o mid Washlngtoo,whesm It ahould hatve b-a stated tbat did (C w•,ma saef.wrt jf &6. mrs vgA*i.as" Wmbdmgfse; a•ad tt " h Ummd L-Aws Pateat shored be read with thin oorrec~iecsUMI tbat um us acay ooforum to do rciord of the e.s in tl Patent Om€m.

Bipged oouankwped, mad setled this I" day of October, A. R), 1900.[ma•. F. 1 CA APBELL,

Q. H. M:it:mmw;mw~ of PfhIw4..

167

N&. 693,934. Patseted Oct. 2, 1900.N. N. WASHINGTON I.A. W. CAPY.

ATTACNOENT FORN BARRELS OF FIREARMUS.

'77

~, . -. AV

xy ~

j68

KAIS. KO1NlGU PATENTAMT.

PATENTSGHRWFr NE- 5478.

169

Translation: Patent No. 5478, "Device for Silencing a Firearu'issued to Josef Hutfless, I June 1901, in Vienna

The proposed innovation hri3 to do with reduction of noise due tothe sudden discharge of propellent gasea after firing a wapon. It ishereby claimed that the barrel will close after projectile exit. Thepropellent gases will be released after passing through two or moreregulating tubes ruiming parallea to the barrel. In this way, thepressure will be reduced and the gas exit will cause only an insig-nificant noise.

The invention, for application to sporting guns, is shown inFig. I through 4, the sketches showing the longitudinal side view andfront views of the barrel cross wection, A-B, of Figure 1.

As is evident, the mizzle of the barrel forms into a funnel. Atthe bottom (;f the barrel, a, are arranged two parallel thin walledtubes, b and c, Viich are connected tog-.ther at their ends.

Tube b is connected to the muzzle end of che funnel shaped barrel,a, while the s-* esd oý the other tube, c, is equipped with a row ofholes, d.

This weapon requires the use of special prcjectiles which aremade up of two loosely connected parts, m and n. The charge is di-rectly behind part m, %tich is of the same caliber as the straight tube,vhi)e the front part of the projectile, n, matches the narrow p&rt ofthe tube and is connected to the heavier projectile, part m, by a fixedpin.

The operation of the device 's as follows. Upon firing the weapon,the developing propellent gases in the tube push both projectile parts.a and n up to the narrow tube. Arriving there, the heavier projectile,u, will be forced in the narrow barrel (poeition m') and thereby heldback. The front projactile, n, in consequence of its acquired velocity,will free itself from the back projectile, m, passing and exitingthrough the remaining portion of the barrel (position n').

The propellent gases do not pase into the atmosphere through themuzzle of the barrel but, because of the obstruction, they enter tubec through the opening g. From here they pass into tube b and leave thelatter, with essentially reduced pressure, through the arranged holes,d, in thks front end of tube b, whereby only a hissing noise is produced.

As the result of this operation. a loud noise will be avoided andthe propolleut gases will leave the tube producing a damped, unnoticed

noise. The remaining proIectile part, m, in the tube can be removedthrough the insertion of a charging rod.

170

Patent Claim1. A devfte for silencing the noise produced by firing a wapon,In the following manner. The b*v-oL near the mzzle is to be funrelShaped and to this ar to be conne,:ted one or more iuterconnected

tub" from %hich the gases dischargn through many mall openings.

2. Two-part projectile, which is described abom. The powdercharge in to be behind the rear part, which is of the smw caliberas tho strOiiht barrel, and the front pa4, which ti to be looselyConnected to the firs par, wi~ll hvm the some cmaliber as the narrow,portion of the barrel.

171

JOSFF I11IUFYSRS isW~~

Af. I.J

- aZ

UNIT ED Si'ATES PATENT OFFICE.MM&X ]s--- x&XW., Or )A"TIOJW, MrO2!n=TIU. ASSXQOS TO AIAXIN 9=11ME

1Nh332M GIW.NT, 01OV '-'- OSIL. 09 Y.. A COAMFOATION OF NMW JE~RT.

m~a.at Je.bass ?steaL Patentebd X&.7 SC,1910).A3beU.1 X.Yc~A, 0, U4 101t $MIf To. ~4-OL

ne OnR UaAW* it "MM' Coan iin ragmis shah .e sectired witJcut requir-Be it knows thist 1, THaax Faker MAfAxli m .g great labor i-i Ct.' aspeibling of the din A.acitizen of the United Stctw, "ei gijpieissd ýMsng.

the city of Hartfordi, in the .Stat&. of Can- ~ae in 'enf ion rial bo niore fuil; oz.f iedcuticst hae" invented ccrtain new and -4e plained I.- re~nafkr * ith reference to th5 ac-

fit! Improvianents in Silent Fireaiu~i of coinpanying drawin in Which it is Muss.-which t" folowing is a spee.cication, rsefer. trated r'nc!r wlu7 soC1 6aices being had to the scowmpenying &r&w- F~its-re I ih G. vie i.i nidt devation of anisa, forming a part hereof. Iordiziary ~pdRrifti eq-!ippet' with a.1in the continued use of silencer fc~r 'Ire. silerncer w;,zch emhlb't,- ýt inveritior. Fig.arms in which the energy -. thoe pci.1der 2 ig as dc~al vwie%; ist 3lL% and on a largergase is dissipated in rotary or whirl ingwl cle of the silencer- sh own in, Fig. 1, L por. osmovement of the gase beforc the~y pass tntv tioru of the barirv.!beiru_: is-, represented,the atmosphere, and in which a sern;.s of ;*r- Fig. S is a tilce view )t ono .' the dia-

ls titiorna, diaphragms or sprn-aderi. are si.p. phrngrar, showing thae ilu the cir-Frorted by a shell or twsig as; the muzzle o.f Icuinference thereof. I-ig. 4 ;s t ± saesthe firearm, the rotary or whiln no;- ecinoth .FU. h.'' ore casing, 70nent of the guse tak!ag p1c- in tho ciain- Ishov'ing the knagitudinat is.r

he.formed therrby, t~he partitions, d:.&- In tht einbodii.-nt of" t. . ein ,."tion shownt0 phragms or spreaders nafrest the true muz- ini the drawing theui 1:, - curcd to the ex-

zle of the barrel of the firearm are exposed trerniity of t;.e bitrre! ;i c. thf, :110, in anyto the highest gaz ]r saure, while those more suitnble manner, as by seepw tar:acls a cas- Isremote from the muzzle are exposed to much ing d.Ihc .peeal sub.,ai~ycrless gas pressure- Lighitness in the sikcncer cu bAr in crresit section and of e<. er or Las

25 can be sec-ured by roaking ýbe partitions, dis- h rs!ýV& as. may be requis ed aauf tzU i a sfu-phragms or spreaders in the zone of high jport And inclosue to- the *;rite (J ring~legra dpressure of sufficient strergth to with.I silencing devices or rdirtitioms or diaphragnss sostand such pressuis and by makigte A- j .r spresaderi e by w~hich Use gasces, which es-titions, diapham sor sreu'ders more remote -A pe at the Ptuis.e of the barre a, ste ,orn-

so from the muzzle of t inner and eviii of Felled t4. acqu ;.'e witihin piccessive ceils orlighter material. It is found, ho7-ever, that ci.Aw-!r iormed by the diaphragms, e, & ru-it is necessary to provide an abutment for iar or wheirling miovement. Ithe heavier and. stronger diaphragm.s near 7zn the embodimecnt of the invention shownthes muzzle to support them against the im- each single silencing devict- e is general~ly

15 pact of tiar gases rind to relievn fnray givet circular or annular with rceference to thespressre the succeesive lightor didpbrams axis of the Lhell or casir~g a, ind is spiral orWhich are lisib'n to be crushsed eventual y if coamehoidal ;n cro-o section, an opening d Vthe resistance is through them. !.*~ink fornued for the pasisigt of the pro-

Owe object of the pre-sent invention, there. Jectife. In the construction shown, such49 fore, is to provide such a construction of iop,ýninvr -s ercentric with respe~ct to ;'- axis

ailencer-i of this character as shall ý)ss ca- of the -.boll cr cassng. As is now well un-peble of withstanding the impact of the dersto~ad, the powder gases are directed by 95!ase while at the samo *ime the mmnimume the frudeo conical portion ol: .ah Jia-

ofweighs, in the silencers is secured. Fur- phragrr or spreader, or single "ie'in d -4s thermore., in hilencerv of this character which vive, into, the aiinular Chursm-er fP-r-,re by

airl eccentric with respect to the oxsi of the the diaphzogm and arquire zierein a rapidgun barrel, it is necessary to assure accurate reotary rrotmirn i% which their enerly is dissi- inotslineiert of the opening% through the sue- pated. Pie disiphragn.s or swpre___ ers, as el,cesve diaphragms for the passage of the nes"a the nucxed of the gun are natu~atil

of preojctile, sub'ected ~o the highest. presure of ileIt i~s, theref--re, a further object of this i gamest, uh'ieo thows more remote- fr m the

inv~eution to provide a cnstrue-tion by which I muzzle art, subjct~ed U., a cornsiderably lower 105sugJ1 atintinent of the pesxanugs through the I presurv.ý 'I'doee moon- rtnote from the

173

Mgadaul of the Cu ma, therefore, be la proper relative umito with ths o'Cen'iII&CpabieG of z~saighirmw piremure than thn 4' in amunrte ne=s viCS the borenewm the muzzlet aud may be made of usuch the barrel &ksbtar sbeet sftee t"a thtee near thin I [clim Sq mnyinvention:nmwth, or may even be mad.of cA suminete' 1. A 4ilen'adng 4evie. for fi~reanra, com-n.swhile thorse neser the mutak are naeed o1 =r.~n 4`1 t lOr Milking, a sewim dmetial. However, ahouid the diaphrafma or prgnsor spreadem dispamd in thef adhellsprtesoIez neareir the Muztle a'ea 4iai 11r casIng ote from the Mazzle amd fa cM-11149144t, chow morn rtaytes frem the Muwse 1 ang Is 1148M11io o f Jeambers, egich of ta.me that the latter receive the preasture trsn. 1 diaphragins or .-preaiez hariatg an opeIng 76inittd atrougb the formter, they wou'd If-or the lianmge of ahe projectile,, andA MeS-eventually be braken down. To .tbviate lively beavy or uAmeeg di-sphragm orthis, an, abutmn~t is fotused int this Phell or op.eaisler di-poaeJl in the shell or casing td-eeawg d to receive the preauD? of the din- isaont to tht mustsle of the fimrear end a06o

i~phnguaa or Spreaders wn the zone of high loivinjr atoenn for the Painge of the soSax premiere. Such abutnwct~t niy be war&- projectile, tiCriTdI or, CISUe having anousy formed, but an a nvettieat, ~And imxu- .almtnient to rveest the iorward preaure ofpcnaijwe, but effeative construc~tion, Use "bI s.uch Leavier diaphragm or ipreaiier, when-.or easing d, afteir the lighte- din phra4,.w or by the lighter diaplu-agmn or spreaderswws"reaeie 0 bave ben placed thereans, is rremote fromn the tottaxe of the fireiaum are(orined with An inner circ.urafertntala ndgv relieved of the premure of the bearier die-

Cashoulcier 8', a by spinig and against phragzn or spreader.suitch abt'rrnent the heavier ;iphragrmas, ! . A silencing device for firearms, coat-spreadern *1 rat. It will be understood j1Iiung a supportit'g -bhell or Casing, aL seriLb"ha the number of heavier or stronger die- of diaphmkmist or i-presiders dispoied! -ate9phragnia or spreaders em'ployed will depend -h-11 or casn.Mg remiote from the muzzl andUmPOA this Character Of the guO t0 Which thes4 funning A 4LCX-M0UCM ot Chamber., each ofsileCr is applied Fc~r % ght power gun tedap gians or spruentoaving an open,it is sufwiet aio prvvidt one .esv,-y, stool d~s ig i.'; t: Ph am of die P-",-04- and

$a pbragm or apreader e', as anowu in Fi 2 foring an iinular cell suetatiy con- 9of the drawing, but with it gin of hi;We choidI in o t awtioee, ada b-svior die-power two or more of the heavy ateel din- phrageza or sprrader dispoised in tae Lhell orphragms or spreaders may be -eqnirv-4. Of .-Asng adja'Cent to the Munkl -f Use firearm-XIMe the number of the ligher diaphrognis anid .1, Ii viuang "pening for the pamage

S& ci sprieadess einployed will also depnd upnI "'f the projecil and al forming an AO- 4the chararter of Mee gun (a which the n-. neil-ar cell a leetintislly coneecloidal in crowsleocar is applied and th effw to be pro- ~tuthe supporing "hl or casing hav-duo*&. In thee comstnrution shown in Fig. 2 i jog an anutasent to raxivy 1 -a pnuaue ofapses a provided within the aehel or ezuing wichi havier 'iaplaesgmni or op. -,ader, whorv-a* for mrew- than one heavy or strong die- Ibi' the light or diaphi-agina or sp:readers re 105'

pbr~iu orspuderazd aspe orsleve40 eou fromia the muzzle of the firn-.rin aroma%-itt inttdoid to hold the single diaphragin Ne~ved of the p'r~e-ure of the heavier dia-or spreader in place. I hl agm or 'presider.

It will be understood thatt this pro% sum & A %ilencing device for firearmiL, can-4& of an abutment for the hea-.ier dieribragm 11 using a Sul porting *hell or caring, a artes 11

or spreaders is equally. desirable, 'w~~r of" diaphraguis or spreaders disposed in thethe "ienceir be concentric with the axis of -Jori-l or ciming remowte from the ruszzle ofthe gun barrel or eccentric with resrpect tliervL- t h4e fireenn. ea~ch of the diaphragms orto. in thb cornxtrucl ion hhown in the divw- i %prwei~eris formIng( 94~ al.nuWu o-1l %ibatat,-

so Mng, hoirevor, the silence is eccenitric Aned it tiasli Mcwueloidal ine sr~eas~on) and having Ilsthenefoist heeomee denirablot to preside.een a lin .eimg (or the pamsagvef othe projosictile,fir- reachitj amuiring the accrate al~nentent a~id a hseavier or ftrcsngtr tý:-ephragrn ca-of the openingi e' ii-. the sevieral diapbra sms -prradrr d;-4ueed ini the shell . ca!,ina ad-or- aprvoadets with the bore of the gun nr- joe~-nt to the nIeUL1ee of Ishe 6r~ Tandsio

as reLl. 'or this purp'vae, In the coewtruirrion loinnitig an annular reel qubte!a~n+Yilr ova ýýibssown Each of the ýdiaphragmsnao si- arundert; chtuedal in crosm toaction and h A ii , VL"44i-is provideol ;a its cirrumif.-rren w-ith a ker- itig f..r the pa: sapie of teet ieb, tsP,way, &I 3hown at as -z' Yxg 3 auid the sleet) pi -ztiuiig shll1 or rauinE~ having an inte'ruoror"neo is provided wiIti.anh inte.-nsi I iicumfer-rital ridge fowrnin¶, an abutinenteoovenientjy fonaised byv rolling or Iprftzinr~ 1hrogrt -ii- sp.-ad.r. vb.re-ýv the ligbter dia-11 suitably Lhre ookl into the wuter wvail of pihragmsi ejr spreader* rxtroote frk--e thethe casing. Wiih this iccestruction the din- 'reusile of Ilk* fire-srui ame rrlierv'd of thepbragms or aprvdce-s cannot be ini ntro -cd prnswure of the Leavier diaphragm orLotos the &bell or casing except in Vcesr L'prvaezý Ii- SO

174

-g ai k

4. A silericing A~evive for firemnun,u. cohui- j ig a 3bucce.;son of chamberis each of the dia-pfl.Ling & %o'pp rting %Jlci or raing ard a ;'hrsrnii or %preaders fnrmning an annular,eriu' of dim phrlagms or qpreadeM di .ur,.s co-ll i*ubstantially conchoidal in eanV44 ~twiciin the shelf or "eang maid fornuajin a futm-s- and l~ixvng ma opening ftcentrically di,-.

9 5 ien of -hanibrs. eac~h of On- tfipl.ra2's jmwrcl for the paitage of the projectil the I*or spreaders having an oix-ning ecccirie'~lly -hell or masing having an interior ridgV. ordLitpomwd for the paasuge of thee ;roje-rtilc. lce) and each of che disphragim or sprradtnvlite ahelt or cainsi heaving not Itiaerior rrdgu, hewing a key-way tat cnipoerste them-with.or key andi etc k of the dmialpvawtni or This ltpccitkataon signed and witnemed

10 7preafers having a ke-y-way to ON0wifierale this 274h day iet Noiernbcr, A. D., 190A.

.A silencing device for rt mt c IR MPxC'nAXMpr&Idng a supporting, shell tie rasing anti a Signed in the pre-set"e of-meries ofdmparagnis car ~jm.r4all<i pomd JuirrmN~a IL .14zix,

If in the suipporting %shell or casing and form- i La%-& E~. Bzaxwrrvao.

175

ff. P. MAXIM.BILUT FISLA1M.

"UPLICA?1OU ftI.3 NOT.$$. 11".

958,9~. Ptente Nay 24,1910.

Atts Inventor:

176

UNITED STATES PATENT OFFICE.:111amIl muRLiM or Pxzjor". £WITZtAL"2D.

M11vzCS "Wu TEXZV suipaMi 07 TUV RMPOu.? OF rMrazRXu

1,000,702. sposilot lotae LAttiea atw-! Patented Aug, 15t 1911.

ApfillaioUn W" X*reukt 9. 191iL Serial Se. I303.

ll ifi1 wrhom, it may coqc4m: ~ e in'd. ,uhlm'aaiimd am]i it is noade for two).lie it knuavn lta 1, Ft (ic Titalizt-m, a third, --f ii'. imm'mglm sf hit#. net-nork(. t'me re-

ciotim-rn of thme Sw"i Co(oemosirmtiort, resimding folaimniiing thi"Iim bis.go, 41 Aisnt na-t.',. Thmeat Fribourg. of the Switit (Cnnf~irernti o, dis- , a'Ire toniciliv enla-g-t-d tssward the

a hame inv-ented .rrtain flow and us-4-fsl illm- fti-sitm ei-i. Th.11w I;I1riin n-ar pull'. air till eajrovernins. in IDavive., for fltie~5I .1411 remonlf uruewd ttjsa~rJ liT-- wis-rs t, amid c'on~liltatvmf time Iteptir miof Firtearnis. cli wiHi I tile fllt- lopellief 1 t-mmmi ftso ithe 1111144-1.1 1'. Till'

iow~itw is' a t~lecifical ol"l..Imt . .1 iaa; C at Iif. "riist e-mij isor -lAmThais invention errlate's Fs d-i-6-,es I )r fv-n.c. t iar.m~mm olob s pa.'-- (wsmr nftlw / limm'i

10 offing mCu vit-~oat It( firr--a2-mL~ Ats~ilm till Iti.- 4mjs min 'p 1111M tiis -1114 ervilag to~to tlimisa inventiaon time ruserqn' A ith It hich tihe ;:miama~inli thme 4lri-%es J at a givedn d.:i'famgawwa of cvinihAion travel is dm.,tm-ued 1y fromin s-act t~hmr hit. that s-adi two succ.44-e'-

C iding m'.id gaimmem through a certain' nuni- ing Ivrtre' fmrnas to ciarm-es passage for trioiwof cmanmlernm which are arransgedi at a cvoumprt.-'sd gm-.- Thse o'ise e' is l-urrvoun-let

If certain dasi.-'cm. sport the one beisinrvhe lb.I- a =--^-nd tamia' j~ of a greater thammma-imr Toother and wtoa-- have pa'mgayo (-or the pru. timer. e. nIII# poisationm of m ithih is recrostarisjectile. Thme gasest are ti~w' dlm-its~te frkman tAit r'tirii to tbe -- n*msiawsm axis of tile tublu-tihe t *rajectncrjr and inade I-) exiiastid gm-ner- lar dm.em. . Thisi tumiw oJ it; prfsmr-attcd .tally to itad C14laamnhe thea fir-'t pcmt 9' for t-nm--timird of its 3m ngth.

so lime deviees accoording to) t~is invention A thmarvi Itai- A ixerii..raasd at ius rear part 75differ front litidevric-es of kno~wn t-m'and (sr one-third of it- i.-m-tstl Nuarrounmisafilesrving for the ,..ane pairpmese by the ar- tamise ,r. Time 'Jart tat'si-n v, and A m'. filed

rangronent that the bAid espansion'cloamniwter fle im~winL-,; .4 ntlm.'. Nut-li as aluinimamiumm.bute the -halw (if clsrin-ic~t.al r whic-h arm- III..- (I ~ m~sf Oil,- '.ui ". k al-em c'tnlris-

S& mounted in a caising lime rmar end of whimm'h I% i li r. rsni oin tIm. a m-s tif file ,sta-rmcs. -4n -ýI)is tsrrA'ratosI or fm'rzmmd s(Pf a-im gauze for 1ith~tl zm themt 0mmc time d wri-mam forf tf itti Iengh. The inner caitsig is fur. R G%' ssmm'lfint-sr".ther inchm~s~ in on* oar nvmorm- Inim~tial"m tih.cim -IL, fin lii r,)1(, ramd ism- time .nm~r.o

3a re alterrmate'I~- perf-srat-d as fihe frmmamt mat ,u:. a- -l-loa n 6Y tife trramw,. 'jima ;slijtvtile2attime tm-ar end. 'lme a-A. Wimad arv c-m,an-'. P, in I-am inj! the1 ki-rri-I b, eimter- into thmeptrm~sd at a I-try lig degree of prv-'emmre ivomwml Issitiom'. Im' the IiarrOW 0Xtr.amit ms-sWiten they' am e trrieae w hso t,4.%r iýV:Il h"llI h

Jib the acvsammajsanving dirawinmg. ma ulila imf( tlest gait s.-. .p- titma-mblme nakri'ow Oipen-

excuion of theolomve 4. ali nmnlelam - wL~'-, ofI,,ir,t.f or incai 114 #fi40 Fg re -rpsr.ýramta a horivimvtal Im-tigi- 'mm-icr.- it., L%,~ 1; lir'' -!tts- fromm em 'wmamding 9

todulmvio f timt aploaratu,. rimg. --, imistaimlli owwa; oil file Iilm1.tg of fix.-tat Jmam -show a -er" imooz als-wr ubh. line 11 -11 1" f". thss ve-cilwq of mzm-. tisrassigh ite r io-m-n(weFil 1. ICm-.m 3 an,! j lisa-. mirferreae I fl~'N in Ott. fill- A fakj-e plain mamlimomit anyto the ela l b.ofth diems shomwn an Fig's. r'-;sort 'Ile, 1-ý ml all -f the. fmsrwmrs- p~am-:

.61ad? ig- ill 7 bbintholie dImi.mit o iI, n (i c mIt~- m k-%lint .h 1m-t frk n n siler- 100tharae rnoi.ifi(a!ju~n,. ifi Iim5 :s~-.-, t- d 011;%. V-rap.na low the ven-

he -rsmmtr nFg.. o4lmi ?m-a? 1.m:sc) Woless h-t's.-,!4. I line nwoarea maer s h internal dimans,orr of "wtmih ma el, nrm'att t,-. 'a frrn of time bi.'s-ms. the ir..a

"odIcthe owter diametaer -.4 the bmarreli I.. the ig_ -ill IsI t-mi-mm m -imcrrmle into the60 An aflgtilar alast o' 1mgi 31 ami the fretns- , Amd & t- -r0- l-rc Irs., t ImIr. (

otto tv re t wr to fix fime do% mc. to the -.-.... 1. 01 Iinst 11Cts- misse e 'is'- 141barr-el lo, scaid molsm Iimeni isu~ls.IOint er aim. I tssmi.'i 0,#. ; 1 ,s f tie mi.-' q at m)(I imirsier

sihc. Viae aitaermur otftile apiparatt., ma Jmal mmrm mm !i (61 o--'m of a few nm'l;-provided witha a ars.m bf tuhb-dat ailav-as- 4 owl-rr' 4tlsrcn oamid i uviijm ma npi-*-raarv

8# placed co-axialy in time tube o- Thua tu~h. low ai64 trxt peaaagw of this gaat aromiamd the 110

1 77

9 1,000,702

tube e. If this tube werv to t,)uch the tube tIbc projectile by nseaniw of wets&.utire~evtile resut. would he a pressure ona thae pa.- iiieaas smhich fo~rm a channel for the pa~am~ga 2&p'ctahe C.111z~ing tile some to Aleviate. of tlap p!'Ojectile. Comprinuing ini combination

Expera'.iaentas hrve shown~i that theo reo'il A z'ertalfA $lumber of Cle"Ients eonsastalag; ofto(f a 1;un fitted with the aboic de?.crdib2 ala.- icion -raI slcevc, u tube inclo--iaig iaid Oe.

V ue s oil y %ory ,Slightly diraiiniNsihei, the utt-tats and pearforiated fo two thi.di of Atiautomalitic kicoia~ing, by recoil could Itacrr- lvaagtha fronatlaue front end to the rfer, an 50fore bie ftor'vsM'.eletau-c cUsin~g surrounding said tuha and

Fitz. 5 sIaowe5 a naodJiliell toaasraactino PC- C"I caipy-y-~d of tive tubes of which the inner10 IaOt'lifig (UP i.hi.h elat taabajtir slereaic are a.maa ui ierror~Atei r~t the front part about one

daffe.rvitatly shalai'd thasia ir, thla first itaisliaae. thiard fat iL'i lca,,th, Whe outer tube, being Twr-Acod'n Io Fi' 0 (lie tulxM g on 1la6, de'- fasteqi sit it.. rear Flart for Axout, mne hird 30

waehs eel Suppressed. Thae entire space of it.% leaagila wild a filling otflieatil aIhawizagsbetvaeer tile tu"e e' and h' r.; MINIe with in thelae j'betwoWn% sdt ubes ZiAwt~anr.itily

16 w~e~al twhavitig-. A net--Aork A, hasq llen a'., decs-ibetl and ihiown and for tile purIpnoeaple o thn, insisde of thev lx.erforate4 pur. w~t forth..

tion of th~e aalle A'. Fig. 7i Ohows %lots A, In %%line-% uihereof I have bereaanto sift 99provided in the tube A' for list ftcape of nay hind in filec prewnce of two WitnesyWq.tile gas. V PET U L .

20 1 citim.-- U E ET U LIAn imparoved de~vic~e for leiseraing tile a-r- Wiitne-Ses:

port of fire-arms in whicha the coanpresa-d ALsek-r Dri ,rm~wgases asre deviated from the trajectory of If. C. Cozr-

E. THURtLERDEYJI OE ?Ba Mr. a6~C su m ow or ) 3sE sO~roF or2 &m.un

l1,000,702. Putented All& 15, 191 L

* .10

.9..9- Ifi - -7

1%d7

179

DEuTrsCHES 1MECi

AUSCEGEBEN AN

"IAY 1.6I' 30. APRIL1936

REiC HS PAT EN TAIVIr

PATENTSCH RIFTA~ 629404

Ki.'A~sSE 72a G RUPPE 2E 4o404 X117ze

Tog drr lidauatmmin"Ag Obn die Lirtileu@o ars Powtea: 9. April z936

Hans Eissfeldt NfL. in Hamnburg

Scbaflimpfer ffur Handfeucrwa~ea

TI'-a"latLon; Patent No. 6,29404, "Silencers for Hand Je•.p,?ns"Issued to Hans Eissfuldt, 13 March 1933, in Germany.

Sileneera for hand veapons are already known. Geuerally, theyconsist of an elongated hollow cylinder with baffles, which eithe-partition the chaMber or close it off from the atisphere by us.t ofelastic washers. Either way, good results are not obtained becausethe noise, even thwugh somewhat attenuated, al-ays remains.

In relation to such silencers, the following improvement and das-covery is contained herein. The inner chaabers will be completelyfilled with a porous material, such as viscous sponge, rubber sponga,or a 9tlar mcterial. This material offers no resistance to thepassing projectile and closes Imediately behind it. The gas follow-in& the projectile will be forced into the many small cavities, whereIt will be delcyed prior to arrival at tte closing washer until ouchtime as the projectile will have passed through and the washer willabve closed. In this manver, a suLatantial attenuation of the noisewill be obtained.

The objective of this discovery Is illustrated in the followingsketch.

Fig. 1 shows a longicudinal view cf the silencer in which thewlls, d, separate the hollow cylinier into separate chambers. ThechaaJver, b, is filled with porous material, followed by packing washers,c, and the elastic closing washer, a.

Fig, 2 shows the view of the muzzle of the silencer with thenotched closing washer.

Fig, 3 shows a view of the silencer end attachable to the barrel

of the wespon.

Patent Claim

Stlencer for a hand wapon is described as follows. The closingpacking washers in front of the hollow cylinder are to be made of amateriel MJnch is capable of closing the hole produced by the passageof the projectile. One of the divided chambers of the hollow cylinderis to be completely fllIed wiLh rubber spouge, viscous sponge, or othersimilar porous mrteriil.

181

Zu der Patentschrift 629 404Fig. KL 72 a Gr. 28

A

Fig.32

(01Amngiehi # ',,mp B

Flexible baff les and Sponge Rubber at the Silencer ExitGeixmix Patent No. 62940)4

k82

Potuutt Auw. 31, IBM 2,48,82

UNITED STATES PATENT OFFICE

Wunes P. ha.... Wat Orange. It. J,. sasiewe"I BtuI ?elepf.. "Ilhrlarat"IM Inc ea""ed.Now York. M. T., a ceejo*tle at New 7ork

An.mtM Odeteer 26.11044. "NIs No. 11"A41

2 Claims. (CL 85--14)1 2

Wb' inventlon reatcs to fireartas and more chamber having a rear section 12 and a frontpeitl'ctlerli to a silence for reducing the mwzze 4ectioa2 21. both eonlalistna heat absortitng ma-

blast.ttrrial. throughl which the bullet passes with m~n-lb. Principal object of the Invention is to fmuin cleafance. The side wall's of the rear

nfdiaee the 93oise asiocitted with the muzzle blast 5 zectlion 43 are forined by the metal tube 14 whichef a firearm-L Other objects ame to reduce the is securely fastenci at the rear to the aperturedweight. size and Cost ot a silencer and Improve end piece 11 and at the front eod is Internally&be stiability of performance, threaded to receive the ap~rtured conne-ctor IT.

Important factors In silencing the muzzle blast The heat absorb~ng material In the section 13 Isof a firearm are the rapid cooling of the power 10 In the form ol a number of annular diecs 10 ofgoUf andi 141- reduction of pressure before they metal screen stacked on? upon another and heldemierge. An effective silencerr utUl-=g these in compre.-slon by the connector 11. The endp1inciPles ecomprises a chamber containing beat plece I6 Irictudes as an integral pert thereof a?.absorbing mateflal through w'hich tMe bullet intern-xlly threaded collar It which scriews ontoPaLSe. The effectlverses of suc-h a device de- 15 the threaded mnuzzle of the barrel 01 to ho~d thePenda. among other things, upon its croax-sec- silencer It securely in position.tiona area Applicant has discovered, however. The front section I I comprises a metal tube 2 2that the Importance of haying a larg &rose- securely attached at its rear to the connector 11.sectioal a&e diminishes considrabl towa" the threaded At It$ front end to recietwe the annuxerfront end of the silencer. 20 en~d piece 23. and fiUld with annular dl-cs 24 of

In accordance with the invention. therefore, metal screen. A forward sight 211 Is providedthe Chamber has at its front end aL section of at the front end of the silencer It. In order toreduced crem-secTlonal arm. Weight. size end save drawing space parts of trie sections II and004t are red*uced without seriously affectin: the 21 have been removed. 11Iss. 2 and 3 are cross-efficiency of nioise redu~ction. The silencer may 23 sectional views.be built as an attachment or, pref-"vbir. the re.- The effecitveness of the silencer 19 dependsportion of the chamber may be built around the upon Its length and cross-sectional areav. How-barrel of the firearm, with comnmunlcating holes ever. applicant has found that the cross-settionalthrough the barrel. The heat akbsrblng material area may be reduced at the front end of themay be mnetal screen, which may, take tie form vt silencer without a proportional reduction In Itsof apertured th~cs. stacked onte upon an: flher and ability to silence the muzzle blast. This l.t duepreferably held in compression Platng the to the fact that the powrder gass have %dreadywcreen with some metal such as Uzi before punch- been considerably lowered in rtemperature andlng the discs will Increase the stabillty of per- pressure before they reach the front portion offormance. 34 the PlIencer and so It takes a smaller cross-

Tbe nature of the Invention will be more fully sectional area to cool them a given additionalUnderstoiod f rom the following detailed dea,-rip- amount, Therefore, in accordance w!'h tWe In-tito and .by reference to the accompanyitig ventions. the front section 24I has a smaller eros..-drawintia. In wAdch like reference characters refer sectional area then the section 13. Furthsriore.to similar or cojrresponding Parm a&d in which: 40 the original ieMclency may be restore.d by a coin-

YUe. I L 0% sie vire. partly in section. of a parative,y sl~irht asedition to the length of thesilencer In accordance with the tnvention at- silencer 19. Thvree results however, a consider-tached to a firearm: able reductio In i,-elght and volume. This re-

Pigs 2 and 3 ikre croins-siectiorial views, to lamrgr euces the coat, of the zilencgr and, more Iimport-scals'. of the silencer of Fig. Itaken alog the " ant It. improves i-he balaxwe of the firearm.hnce 3-2 and 3-J. respectivitly: Pigs. 4 and 5 *.Sow a modified form at the

PiV. 4 Is a side view, party In section. of a silencer if to which -he rear section I4 Iis builtenoodifted form of the ailener of Mtg. I In which amunud the barrel I I of ~he firearm it. The sidethe rear portion of the chamber is built around wails of the section 21 are formed by the metalth.- barrel; and 50 tube 2S which is closed at the rear by an end

Pig. 6 Is a cross-sectional V'ew. to larger scale. ptece 20 securely fastened to the barrel I I a!:dof the silencer of Fig. 4 t~alen along the* line &,-%. at its front end by an. apertured and flanged

Fng. I Shows one form V! the silerwer 10 aL- metal .lec 31. The section 21 is siibstant&iaytacheti to the end of the barrel I I of a firearm fIllied with heatt abeorblna mnaterial In the formIt. The allencer III comprises a cyllndricAl 48 of layers of metal screen 12 wrapped around the

183

barre II. To permit the powder game to eCtW L A glamfor tAmsm fln mn cpdito aeelabereta aoetlcn 21 ther are provided ah manner of muds, pharalltif afnnular diss of RAW si mcbole as through the wall of the barit I I. flae WaUMet"e within aid Chamber taUsnrsey wflh,~n. tor utar~pl. be drille and, as shoWn. aO respct to the IoMOU1bntima arts thereat, "i d'scarranged in tour row, spacd 90 degrw apart. 0 beiW stacked -M UPon another isf COMM"-TIM dlstnzw of the Anrt hots U fromt th breach soAw and ahut~antsly SlKW sai cbawhr a--of the ireamu It lamgely determines the MUI*d cep for aL p-oagwsy ther-rmwl prOmtvelcity o~te bullegt, mwumng a give neighrt (t onW Munimum clearanee fora waist.bulle and a, sWm powder charge. It baas 2. £ sllrwer tn accordance dli clot I tfound that, in order to save weight, the oatr` 16 Which Said dicta mm plated wItM tan

N dmeter at the sandard b"end may be huncd wawsnw P. WAS".down somewhat without undulY weskenirg it.As shown, the srctn JIT may be cccentutcally ACZJECUSH am tseated, with the auger part under We* bent 'Tin fofloving relerace are 40! zUwd to tbe11, ao that it map be of lazier diameter without 1# mes tat.ti potent:intfanring N,- V h the line at sight.VIO&M A Ml. fmt sectwtu Ut ,Mpu UIlE mewr tAubeT86 internady Utresied at Its rear to acre aunto the Rumba pas" Iheethreaded end of the barrel 11. internaly Uthreaed 221J1 Tethe M ---- Nay 4. 1116at Ug front cnd to recr the annular ad pieceM 1.000.70 Thurlur Aug. 311. 1911M3,; 1nd111le with annular disco 26 ot meta LnM= Humn------ -------Feb. 2. 03l

smenm 1.173lY Thcmtmm - - Wb. 2, 113t6The bcee isreerabl plted Witt same Meta 1fl2Oj75 Thompson June 12, 1617

met., ter exampWe ma tin befont the dir. Of and t,221474 Mas eb. 17, I=0flare punched. It has been found that this Will a 1.40.110 Mania VOe . ismtabawdey overcagne the tendevcy of the discs to 1.497WU Dickman ------ Jani 10. 1gideVeop loos wire ends which uW sla cui~enstllY 1,5726 Paradire- --- Oct 6, IM2eaoe into conmtact with the bullet -s It psame IAU36.4 VOW. DM 23. 1621through them and adversely slfeet the dlsperSion 2^.04371 Bourn J" 91 Ismpattern The boles In the dlse ii and 26 Are W FORSON PATDTSIIpwetrably Made only large erns to Inns'elrsreifa for the bullet Ktaftb Country Thte

Wb W ati claimed is: $10.11" GerMan BSP laps z, 19

Aug. 31, 194& W. P. MASON 2,44U&32

?ill Oct. 20. IS"4

FIG.G.I

FIIIGFG4

FIG S

W P MASON

A r roRNt Y

United States Patent Office3,8911 2

3.l31.~ft tPhr Itiri,,C, ..lt-o,ls of a finle to Wishkh the anti-r.Vloil NI utfjiii.lttf .,It.iitnwentuI of k. invention bxis Nenl appi~ed;~

I~FIFARN4~.I '17ilif AUFTACIII .IENT AN) iIROIIK4 1 (tt'2i smfi'ti fte iucait0 hiHAwi '.'uTII FX,~V.lNIt U. 1). TACIl*,fttIi. lit Sk II( i %no~ w o f riil nt( h

Rkbmar L.. %tolfter, 243 4ortan ParLwa)s. Xrn VoiV, NN, k-itrcd -AoiLnP the hir.1 1, ,, Iciju -ftt to C nicrre front it;

IFftIW U.AL 11,1. 1462. Siee. No 165,334 oI lRAIki I ik a smuiXr ýocov %howiiiy suesi~ t,Re

It Clianot. (CL 90-14) tc o f C' rrt ing!an] 41ustr.,tn 1 the %&p ir..ton of' the 1xillet

Iisi in%ertticn tis 1-v 3 t..-cI comifiitiotin renrir~iltv I IGI '91 4 1s,t si.I., ovw slsuwitsr a mill Liter StatecharacteriteJ 2,4 ,s firting r-'ce. at low rvtrItrit. a rile, in lIh,- IN 'taiiii i. tctu. nonkl) iit 11.1 ,er ihec Iuirge

14bwh is s.rt~c~larl)y ajaps~ed to the firing of ;I hiiL I'.stfct gwiiiwit 1,. -,soovi It-'nt the .,t..ýhni'cnt Sol~ itith Iilp hukh-i-Al husk'. shot. I", tol in Ow o. h~.miI..slincmnrid tr-p.Pfnl Ithe iset

Anotiher 'Jm*,it of 313 jinvenici0 inlt.Atte noti 4-1 nkilthi.I ft-. A ~tofof pokiino .-. ;h s b Iul!<ktootith A '..eit lotrir'.o the the s mt'n o nictr n! N his tep,ciun h1%i its pfinverang~e. accui"- and re~twl re-lu-don tit the 61ti-1p roec- tit.'t mi :...wko-.ion %itthitlwfiiirti ,,fhii.L ltlIt. %h

At it -Aei3 unmteimmodr in il.'. art t tore( Ows !the n ; ti.da iftfgt tsu lti,.9.tcJ to *ik flitxm in dtit. Juia.tntrip aitastteujof &x buillct or prrqe,ýtik at the nsitonwn i Nirtf~r st-r. ~P 11- tk. t ýernonttou. mtresses in the bullet wn f~rspo~,iit %Iith .:..us As 11-7traterJ in I R's 1. the, t':utt'I 1 of at line. forit to try to mn'.e ofr it) one, mide or the ottecr vI theo ivss ri .r.1 -l i, "'.* .s -hi sif a s.iituf' raftJ Kt~rc 12. msIts-baf the hove v( Ot? oo-roomnJd~ tit tuots ', .. , IV cm.iw it 101;1.111-01i.. 1-14, th.. I.r-,ni *I-i.-nrtvrto tobIle vor yaw a.s at rosiss dlutn Ofr turc anJi oi.uie IN-. 1, 'Ai.?L-3 istt-.i :1 -Itt.t .tiii..f( 'i'I iiit3fromn jit 2t 3f 41 &I.01 is switroJ uri,iri~t 1k i..d ev of itie

sitWv the Conottritional butitl~* IIJmaderM lti%(Ii. -Mf 1i4isigit~.ý r 25 *lhs, %M'i~iI hi e no idc of antyAntd tIutWII: so tt-.t Iti %J11t grren.ili, mnr c 0,r vit.nr of t4 Il r,. f.1 ca'. tcAiiA;%' i. Ai.if'Ix to, thu putguýus. tmijthe Iiae~ti of the firing~ ruCse. thewe cro.,ntoiu sIresw i4s.1 -.it, 41 * .. ii. i;ruk s ist sh, s,Kb o, uwe .n 'h,4(314119 it to Kxvneu d,;Gwrwt,4 .. f.1i PiIt- d.n,-.3I 1*"~ no If .. p - 26 Z&.in *%- rn..e in tirioos tilini. 1,.:t ;osits extit fronm the b'ioct of the firing g'.e.: Ihe ),'ulfdetts * J'st ...tis4 ' s'lr. 'I I,i Mt-.t andloof i~iai 'iiithew distoetviie or Woiti'ng ;,nJ o .sLedI o"Ui-d .. 11A. ed.m- Jon ,IWfts -ill: ".'I- Itio It. 14% to Cj' IILI .iNJ i~.u~ t

fog: a ts~uht.nt utijleviaili i.sttaIl r..nire. 0i.., ru.1

. -s Is IeA. l-iWorn If 1 11. k to,. upt I Is itmu'd.Thi'-.% '.dix^, tiunde..rd ,tidmton'., ant .Ic ie. on. cmcm,nt.I. or ..tlxf-w att,h.I it. ttor j'i,.rlise, flr.'j..r

mrased the .hZkotrw the ftv'.nrr; %,urfAxj ot ihe i-uit.-lle s .. I,) lIns" 4 tupnili ..s,.cill 1% rle,qq lIt jitintilill relAtlon got sits 0-CrAil iergth. A. - fis rsi Ir..,fto I R;. 2. tIN~ c-ivietn.,i 4-iciru r cif the

An tsn.fimiafirf't iofti i .eo0n I frr~ts--e Lpu~ is tiir- i Is a ij'#OhJ I's the I-ro: i4 theC ran<t tV 1formeitherA M11LW1 &ttn Wntt Four ~t'iii.Itk .- tF,.h'nr t. the Ik lii C1 tk -- hk he i'..Ct f I'f -o.i* 35~j~ir telf 2.B Iý if I-ertm'utyle of A rtif. five rt.imipk. s-.hh p~i-k'hes s J.tu linst? s.t 1 ir 1.1 .. "1s-n (Lrntl .1% (o *.11~ ' Alls"-k ,sntoil tft tim.-It the ralk Iftse after its% Ct ;hert,on.4 i-cs oti a s.iu .. ., iiit :." -t,:.t~ 11 4ei-trihand ,eeitr.itkin flown it. I't, *. Il Ilk i.-1 .i:6. .. %,I*fl~- tl~- sni ltV~ni~ijl

Al 'it.n., d .otfoit.. in! rel..cJ tieithl of hulis Owu u.Iii.~ un .- I I i.- it L4-ti I In th1k n.'IAtti .I' ", rre*to rediodj krglh, 'N're.s.W .l '(t~ -fti i ti' Jie to I.. icrot ui.i.- I. tin ,. r..s .,ist it. Ikce I he Nteft

mrescs N~'..,e..t.J I.m tt ii... -f tOw I Wit Iriotweq pfreIvr %S~i. p t. - . t *ii ..Uiws gt..iiiJ %.;th INu- uisu.jin ttlt~ou1 Ill It. .se~Iktioh IeW i1. t1h7 %W1u1

1 ijfin. Cspiu-Ws .. wt, '., itl it- i'.J -. p. orut stsIswr

jnmhuu' 01 as,Ocr.it~tm It 11W p ..I.t,,t. ovvt In t..ttis u-usis. In The trio iltjii'r~tcl die titi~rA end 14 .4 It-,- ta4r.tatulilt of ati-hnuentl Jae lit.)- . ..-. tk p'nte nmose KI ý* is 'hot -. rrjt..,. itCirrj 4irite 1~ rot .u

fomtj Wd .0hclf,.ti"iAf itr~.fsM-...ni of n i.the Aihck-et

.5 tt-lir *,~ti.ti 1 i.ftowie .ii~h.,n hnb 16tueu Ahl low toei..--I .ini ti-it-*at.hnwnt mi-.s,-.(iiij thfict,.in .ots -aiu Iuh A busk N,ft.t *.10 flct~aik isIa.. the i- .imntift-rn-n - srrtcmnA glii-4%d it Iiitin, the 4. J S-Sir".It ofi the roil - Illkes 46 i. I1rl.tIvkul ifs.c~-kJ I., i-.iCa tmon .. r

Still Aisothr Qlivt-l of the ,nst.crIK I, !o~ r.s-t ukh li 1-~ hE t. r,n -It .t-pknw-.mar) hirea-h. 3.,NO .. ttAiOhniýrit hi.ifh In'..tirtIk-I .Ith .. 111-1, t~i- ~ n gt .'u iS "s fiu.k 1-tt a .. ir'.i '-s-

will ',r'. to .,(. is trrii, . k itils- flu~'~ iuili f' I - tls: %. t~ . .h his .- n vi.: toi,-,- i t,~fuit..ift'Anwe VnuwtutI. , -t-I j h-, tin.[iit iP,.i4 r , th< 1 tit 0-f r.-r -ii-. Iiti of t-, .,.d.u.tft-I I-ro - f the Ow ,.i~ - t--c ~ lr 3ri~ tiit ish ii.c ri~- 1- -.- y 10 -,1 . .. s.nss ilii. iui.- -. rc i.i-gsun .riJ.1, s.uIL-hiiint 12 I t.1 .ti.~...r --f th. Not, -1-si f~t.. 21 isLý

A luotiis i'i.t i~f'N*t, uitit.t t-.r 4' '. 1". _it th..r tC5( 0liti~ Owt Nt - of tle I -onJ - rit.an vi-howrrinit Nh.h tt.iiut w ltfi 'u-~ "t ";-!-:l .. vi:I :o, I'l 1-f on to i. I.-;i~c t.. it' 0t~s.- ti [!i p.-

kisting .1eftu Itis %)%.nutI .r iis, if..or.i Oxs f.-.L i, .. 1. it.1 1' - -t I.. g-. "A'I~f f-I'l pr~... fit I-Atre..11h I h

irsra,iwi I,, .Iine -r-:l knit ft..- .*% ii .i t !... ir- i .4-f It n-J -- ,t 1 1 r.l~ h .'T ..4-3A p-sti is

Le ur iiib, 1 - -1il' 41A . t 1 r"C "4 .1 J't .It' or,, r I he.l the. 86'.k I-s .

eOthrst q..va, ti.5

.-N ,V<o ,,1 0,h5.koi"-

u mme~~~ifiu t "ti." lii if'. .. 1,.,fsi. .q-. is 14 tint tsfl ii ý , I iin . .. tiin

'Ndi vv i 4ti 1,in, mi-o- IN- It- It,-t -.fii,.4.tiut,1,.j to Iuni4- .

-hr.. c, 1,uini sti 'j fr-~s %iis I~ii~g ..isiiis I. - 'ntuttf. - tI.fn~- .I.,~~~~~ ~ ~ ~ lf I r,0-ItfJ, jIWIk

WhenI 3 ? rrin PC-C' aCCt'eda2nCC At H jinCftiOfl 1:10. 4 01u10rai :g 3r.:L! uJvantart: ofi uiiitarian fe:a-is fired ili po;ci 1c catridgecan.itciac1 in Ittrc of the %iaihcit m;.i..r of th~i invtniion: -i% it %oil.i

Lhe itta m nner peiening! Ittettnidou% La% rrc.'.lre b'e. Lnn~in in hi e, lctp..i*e ga.wsAhc urintehim' .hehuk 2 cntit.ning the !5....~~ The hlit. Ir.!t!nr ervo'Ir'uico.- a:n & ,,-tifi,

bu.aeel iitherefore r..pidly -. c~ckr..cd ilo-n ihe barte ri froin. the,tr- enm c i t erpt.3f ajnid i3.'.~ Iciil C-ti ,(10inth uui mnnr jn m esino uecjir;! tannmci the:,ijiii h exirt rue nt ~ w~yo

11ty x aw skfCII nd the coe ise3 to rt Ct"nditun illu.- f3,.-ht. Aj ilks% t ,:ed in FIG. -4, Ow triirprinv uf the ex-trv"ed in FIG 3. A%%t .. on .' Cie 3.,.k t~iite r.ck-j'cJ rlhi-ýv, pac itithin the alI...-hnicn h)~ th. hut:,& 2E. ;,1-from the di~whiarg enJ of1 the t-airt: 10. the h¶"k 16 l t iti'i'nciettry. i% %W~tflg~nt sin perr-,t the r c,f'-pc~t 211

nni ; udr Ou. t.'r.-, ai'cndt.r: it h,ýh xlit. epa. lit Ii~t* .cit .:rr1 on if% 1C1111t tWore tbi; h..4 , i*t rwti. .

ri.tes sut'i.antwi..I3~troer the r-iccOI 25.:..'- !c- I" rtl ardJ th lv-.-. n it) c I tv rcdlI .. holt te ifthte itacfior iurf,.: of the pir in :ic, .'.c'e 16 1 'itil dott, t-O Ith. flight cf the piro~eelle rcsi,lts fr,,uiit engages the en:r.imv cend of tive conicil f'w-ofn 212. "hx-. 3fwie-'t.si rI1iIt.t;,e,j in I IG. J1. Thm. cjucs O the t-L to. "' In %;x-w ofi the :.Nni drcrvzrivpn ,I oine emt'rxlirten; ofvI3tivcI1v ecceler-tej ith re'3m1 Ii i th rrticx ltie 211. %it In, On inien.aii' itlia~troltig tIN pri .qex thereol. 11 mil.l Ite

that the prnpiet~iiit.k ir.revx in. .r,43) a, ;n it-~ki .'y.r.nt io # 'u itte ,d in the an ihii m...i) of ithe mi .r.-piee ink, the ri~mire 2L. This f~-ioe in; ai. -uriaek v. ri .. ' I.-r~in .t-. U.eJ Cil ha e %2iM~ ti, ih~th. tef----po~itiierile on the apt-,. of 'the 3trrcI mt L %i-. in ail jar from the r.ixel t 'xIeci miter .t thu. irssenttn It s,press fit uithti he Frr*ctile 28 jc--dir%- it. i-Line iii ij rnr-ferfrid. iirxi'rtc. t'.it the -we of rr.?:.4Zsoti :0f.r.-Oefi-om it any uu%Nirf, oil cii et.rc movement th.t it nliy !-0 3'.vt t-.- i.:erimu., I- the il..m ... ilic 'catCii-

Iave lrICit.nt ra'd-d,ý (or gllt-Iitrtie plirpwse Ott).At the .ante tirwe the decirkr'aigd h.'tL IS NKc'.. lite. V.h~ol t di e.iine.1t.

"tmitiiinte~ Of the ev-m Iyr tei j, % a.umg fr~g- the I-.rrd A fitti-rm conlrr..inr zoew~nanmoaj a rrt,,:it.k-. anbehindJ it Stlffi'.-inllý to in:reANC Shelf rIC-sure. jht'.- kr-xast-He. ikt.jO. -t-k li-4 .,ccu.utz to..,. pw.-,cie. -i..gaaei therefore tendi to doi.:haiv ihrixuph the p,,,1 24 at 2-i htiJ. hcir; .up h.itip, -. . h~uirm in end m .11 .. r-A aan in,.Teasd %cca wikhh di-.hairc co,in-piui ark itIMMAri1at of .itkrrji. * i-oat-Ic mtiictl %;*l3 rirranit aakW Au n il~ tcor. .otir It~r~re in . 1(;. 4 .N leiý+t-i- gon i'.*ryei lt... j: a r1"'*.eic [vre. -'d ai fitrOKt-0 rs0vithere the hi..Lk h - thectfr. .mcI .rto th. hue .1.1' :.m ri- ~ n., .n. th, it irm.i vn f tad I .oiel hit.exrx .i,,further tends% tj 1-hid the ctsýart of .%c m~- isept a.v'rtiureit lvi. :rn.1 rai ct'nfrntii rc'jt,:,J u...I sti-thl'Ow?,l the :.its 2.8. b t-,Il he '-ml..'ent. ihetý7fore. ihii 3fl ing! a. ýh~ntv- a. tif an orierr..t dzin..tivqtlc..ifCr thin [,',tthe noirimum oif recoilt .!o,'J" h- it,% .%-'.C ri en- ,I aid N-ve. vnd fl-..in hati~nt a preXjait- ru v exiatIian.et I lt) the momn-git ir) .x~ deccetv.a,,i Cif 'I C ra-.re

3a.ang 3 ji..rnci Je.tt~ thintht - f t.... NieC 3nd

taI2IQY nc in: cr~ot~ rates at% tie~ 0 -7- it mn. fwa~d4Aj a 3,.'tt ji.. ft f.1 fr ,.I fws'peoilk .rin L.oc:~.A" %ekC~ijtyj j~ .5.h,vetL-fA..It~ hioiurt. the roWt. 14t pr'su..i it Gi -%d%. ' jii "Wn ..a.J .m-i.diitig- .

Gouing theCk ito.f %O e .eer lcnit-a i ) .- itjink, hus p.-'' i wo~citrunt irt .. -...d c-,q p--..- "'I3.t I.,24 reach-x the t'aereJ ri t 20 .1 %xIll he ;v.'4uLIit stfli..ýt s-0 husk tot miiimcnwi itio -J- ''conir~w~edi or :I~'J t-~ tib aixo.r~- ~qi. It, -!,.d huk )-.-iF;; .ucL.hcd in -. 1n itr..'..cd into e':~ii.Iition it v-9l tv. ci'.irg-s-.cJ at the fine 0 f-~ th i.e.- v-ih lthe -- I.. if -:,iJ .h~rmtv- ..n~t Iyng CoWri'tc .,NJ

t .;ts throii~h tie tiue Kn-e ti-i-...pt I. ItPc htsL tti.aicd Ki -- J -. nt.3 j'r- irr t tridinr FM.'tnizrt111cing hoiow i..' it( scif ft. dj:fwmi'-le. iltatl& ni tclltt 4' lf-.wv..ct Jod Cuit p~a-lcc Nh~n ih' i .. rrv)ie1e.xtu'.h at .p~r forv ei...nipt. Cart IVc t-wte'Cd C' C Refrteirnw~ Cord in ;he tile ir. `-. r..tgnttr:Kle.1 %iffi. knilt u%~ ih.t t xxii It- (w~. cj. tr.,.,1 h i0%1puit I-orie p.ui'J!t 22 zinis cl:,ted tieb,n-J the pi>tzt UNI ItF) S1 ATI S PAT3\%IS28 M~ims the prwmd -,f s-n-rt-wrst* and) ý -tw oIi So- lit% f---- -----------......0. ('), I '

the ht..). the tigtph.se r-a'c- *-lI tv. i-ct.. '.;s mr(c~~ i 3 ,12 I ý t*r- tt u --------------------- Art-%. li9.'

ithei r~r.tomii'ari. th-wrti-v .rsrr...in: tt;cua inter--t.r~ .' 11 1), 1t~ , r.................--Apr L'f. W~itas pf%"I V'j 3..,ed. -. tv.nr eies'cd it rim hyhirt 2.110.ZO Vinneck Ci al............-hifar 'u. PItt1wtwie~teii througih the p-.'oa 24 Z.1w~.tt4 NI tier ------------------ ji M. 139!.

June 30, 1964 R. L. MALTER

AN' PF,-ECTLZWITHEXPf-NjILE. DETA,'HAULE HUSKFiled J', 10. 0362

FIG. 2

Iý l 24 •)" 216 20

FIG, 328

2 2,o0 FIG. 4

10 10

FIG. I

24

INVE NTOR

fbCI4 L FAA L IfRATIiNI -

A PPENDIX F

RELATIVE LOUDNESS OF DISCREET SOUND PULSES

Presently there existi no analyti,:al criterion for estimatingloudness of a transient sound signal from its pressure-tirnc history.The usual m(ans cf measuring and specifying such signals is by theirpeak SPL's. Since loudness of a discreet sound signaU is's also timndepenaent, it is iinportant to re-examine the qva~litazive signiftcanceof this depende.ice. ', he innst reliable and revealia:g dta are to befound in the co-•,,.'' used equal-loudness-levei contours for con-tinuous pure toaes. T& The 'requency range below approxirn-tely200 cps is of lttle use here, sinice the single cycle tine periodsof these tone are well above that to be found in small arms so-indsignatures. Wit•lin the f'requenry r'ange from 200 to 8000 cps, thelovdness level (phone) of a pure tone of given SPL is approximatelyind-.pendent of fieqcency. Above this range the loudness level de-creases~to a first approximation. directly with frequency. Allattempts to exemplify the human ear by a damped spring-mass system"seem to fail in explaining the above frequency-!oudyiess relationship.However, through i:;ductive reasoning, the whole loud::ess level Spec-truni as described above, can be reprsented by:

200 < f <8000,

LL o Z0 log Pm. phons (•)

andf > 8000,

V~m -30 /! "8 0 0 0

LL ev 20 log . 3 00- , * phons (2)

wherc

LL = loudness level in phons;

pln = peak sound pres-jure;

f = pure Lone freq-.,'ncy, cps.

rThe prrstsure-time arei x.t) cf the positive half-cycleo of a sinusoi'jAl tone in

189

A =rn . p(/?-) (3)rrf IT(3

where

T/2 = I/Z1. half-cycle time duration.

Thus, the loudness leveiz can be defined in terms of the recurrentcharacter of the pure tone i. e. ,

200 < f< 8000, LL, 20 log Prn.0002

(4)

f> o000, LL u Z0 log Pm 30 AO, A

.300Z -3 w

Or, in terms of the positive half-cycle time durations,

200 <f< 8000M Llci 20 log PmM060Z (5)

f> 8000, LL f 20 log Prn (Tl/Z)s) - (T/Z)

where

(T/Z)8 0 0 0 = l/Z(8000) = .063ms

The last equations indicate thai:

1. Up to approximrately 000 cps, the tone loudness level isessentially equal to peak SPL.

2. Above approximately 8000 cps, the tone loudness decreasesalmost proportionately to the tone's half-cycle time duraption,

If the same conclusions are applied ýo the singular sound pulses,their loudness levels can be expressed by:

•063 ns < t < 2. 5 m.4 LL sz 20 loR .000

t <.063 ms, LL * 20 log Pm . 063 - t).0002 304o3s

190

I

where

t = time duration of the sound pulse in me.

This suggests that the loudness level of a soutd pulse longer intime duration than 4ppruxitnately 0. 063 millisecond is numericallyequivalent to the peak SPL. The loudness level oi a ;ound pulseshorter in time duration than 3. 063 millisecond decreases approx..irnatelv as its time duration. This is partially borne aut by therecords of silencers fired at Frankford Arsenal and partially by thewidespread tendency to specify transient soundu by their peak SPL.Aithough qualitativelysignificant, to date the above equations arebased only on a somewhat boldly assumed analogy between transientand continuous sounds.

It is interesting to note that the "1loudness level" (phons) isnot representative cf how loud a signal sounds. In other words, theloudness of a signaldoes not double with doubling of number of phons.The true loudness is represented by sones, which are related tophons by

L = 1 ,.033(LL - 40) (7)

where

1, = loudneso in sones.

From previous an¢-lysis, if the sound pulses to be dealt withare longer than 0. 063 millisecond, the loudness in sones can berepresented by,

L 1 0 "033L([•Spum)pax- 40]

which is dependent only on the peak sound pressure level. A plotof loudness (L) vs peak SPL follows. Here may be seen the truerelationsthip between peak SPL and how loud the signal actuallysounds, As an example, a signal of 102 db peak SPL souxds twiceas k•,uc as a signa; of 90 db, since the latter is half the number ofsones o,. the fi)rmer.

191

500 . . ..

I g

00200 ... 1

40 50 60 70 60 90 100 110 120 130Peak Sound Pressure Level, .SL (db)

I9Z

BIBLIOGRAPH'Y

1. Allen, W. G. e. , Pistols, Pifles & Machine Guns; Lond:)n:English University Press, Ltd.; pp 170-172, 1953.

2,. Bar.nister, F. , et al: "Wave Action Following Sudder, Ro lepse ofCompressed Gas from a Cylinder;" Proc Inot Mech ingrs, Vol159, Wt r Emergency Issue No. 4Z, (1948).

3. Bauer, R. , et al, "Auditory localization of Noises;" AberdeenProving Ground, HEL Technical Memorandum 4-65, 7&y J963.

4. Bertrand, B. , et alt "Overpressures and Durations of Shock WavesEmerging frorn Open Faided Shock Tubes;" Aberdeen ProvingGround, BRL Report MRR-1724 (AD 633 161), November 1965.

5. Bixler, 0. C. , et al, "Analytical & Experimental Studies of Weap-on Muffling;" Ling-Temco-Vought, Inc. , Final Report (ContractDAA F05-67-C-0048), August 1967.

6. Campbell C. , The '03 Springfield; Beverly Hills, Calif: FadcoPuliahing Co.; pp 41-43, 1957.

7. Chaillez, R., et al: "High-Intencity Imp-alse Noise: A MajorProblem;" Aberdeen Proving Ground. HEL Technical Note 4-64(AD 450 726), August 1964,

8. Corner, J. , Theory of Interior Ballistics of Guns; New York:Wiley & Sons, Inc.; pp 395-400, 1950,

9. Crossman. E. B. , "Silencer for SMG, Cal. . 45; Flash Hider forSMG, Cal. .45," Test Sectior, The Infantry Board, Record ofTest (AD 47Z 094), 29 September 1945.

10. DoD HR 2a36023764, "Small Caliber Weaponj Silencing Devices,"July 1964.

11. Davis, D., et &I, "Theoretical and Experirnental Investigationsof Mufflers, with Comments on Engine Exhaust Muffler Desiga;;"NACA Report No. 1192, 1954.

193

12. floelling. N. * et &I, "Characteriatics of Noise Produced bySeveral Contemporary Army Weapons;" Bolt, Berael & Newman,Inc. (Conti-act DA-49-007-MD-885, March 1959.

13. Durnond, J. , et al, "A Determination of the Wav.e Forrmis and Lawsof Propagation and Dissipation of Ballistic Shock Waves;" JASA,Vol I1R No 1, J•ly 1946.

14. Dunham J. , "Develnpment of Cartridge, Caliber , 30 XM76"(U); Frankford Arsenal Report R-1794, March 1966. (Confidential'.

15. Fulton, C. , "Silent Weapon System Cartridge Design and De-velorpment Phise !: Design" Franr.kfard Arseral Relport R-1654,November 1962. (Confidential)

16. Fulton. C. , "Small Armns Silencers, " DDC Dernand Bibliography,ARB032041, 16 March 1965.

17. Garinther, G. , et al, "Auditory and Acoustical Evaluation ofSeveral Shoulder Rifles;" Aberdeen Proving Ground, HELTechnical Note 1-65, January 1965,

18. Garinther, G., "Transducer Techniques for Measuring theEffects of Small Arms Noise on Hearing;" Aber'deen ProiangGround, HEL Technical Note 11-65, July 1965.

19. Glass, I. , "Aerodynarnics of Blasts;': Institute of Aerophysics,"University of Toronto, UTIA Review No, 17 (AD 247 445),September 1960.

0Z. Gustafson, G. A. , "Tests of Silencer for .45 Caliber 113 &.ndM1928AI Submachine Gun!;" Aberdeen Proving Ground, FiringRecord, 12 M4arch 1914.

21, Hammer, E. W., "Muzzle Brakes: I - History; I - Theory:"Franklin Institute (Contracts W-36-034-ORD-7652, -7705),June 1q49.

Z2. Harrison, E. H. , "NRA Fire;.rms & Amrnunitio)n Fact B1ook -Silencers;" National Rifle AssociatiC'n, Washington, D. C. , 1954.

23. Heising. R. A.., and W. P. Mason, "An Inveotigution on Silencersfor Small Arms;" Bell Telephone Laboratcries, In,-. , Final Report(Contract O&i&sr-906 SAC-14); Part 1, December 1943 and Part

194

24. Hughes, F. K. "Demolition Devices and Acceqvrice± Silence--for Subonachine Gun, Cal.. 45, M3A ;11 Psychological WarfaraCenter, Fort Bragg, Interim Test and Evaluation Report No. 1on Project No. 11006 (AD-57 237), Septembe- 1954.

.5. Hughes, F.K. . "Test & Evaluation of OSS Silencer for Sub-machine Gun, Caliber . 45, M3 and M3A1;:1 Psychological War-fare Center, Fort Bragg, Interim Report No. 2, Proiec;t No).11006 (AD 68 828), Jane 1355.

26. Kinsler, L. E. , and A, R. Frey, Fundamnentals of Acoustics;New York- Wiley & Sons; 1962.

27. Lamb, H., Hydrodynamics; New York: Dover Pubaic tions, Inc.;1945.

28. Levin, S. , "Concept and Feasibility S~udies of Muzzle BrakeBlast Suppression Devices for 105 inm and 155 mm Howitzers;"Ordnancýe Engineering Associates, Inc. (AD 601 728), Febrxary

1964.

Z9. Liepinan, H. W., and A. Roshko, Elements of Gas Dynamics;New York- Wiley & Sons; 1957.

30. Lighthill, F.R. S, , "On Sound Generated Aerodynamica!!ty;"1"I - Genera! Theory, '" Proc Roy Soc, A, 211. p 564 (1952 );"II - Turbulence as a Sout-ce of Sound," Proc Roy Soc, A, 222,

p 1 (1954).

3A. McLean, D. . "Firearm Silencers, Vol I - U. S. ;" NormountArmament Co., Forest Grove, Oregon, 1968.

SZ Moore, L.F. . "A Test of Silencer, Caliber .212, TZ;" AberdeenProving Groand, Second Report on Project tNo. TSZ-2026, February1 'Y52.

33. Moore, L., "Feasibility Test of a Silenced Showgun;" AberdeenProving Ground, Report DFS 1330 (AD 350 280), May 1961.

3 Morse, P.M. , Vibration and Sound; New York: M,-Graw-Hill

Book Co. , Inc. p 312, 1948.

t9

_ _A

35. Nelson. Thomas D3. The World's Submachine Guns; Cologne,Gc& many; International Small Arms Publiahers; pp 10, 11. 44.54,98, -ý9, 498. 499, S00; 1963.

36. Office, C1Jef of Ordnance; Annual Reports; 1909-l.,IZ.

37. Office, Chief of Ordnance; "Small Arms and Small Arms An%-munition:" Pecord of Army Ordnance Research & Development,Vol 2, Book 1, Sec 2. pp 135-137. January 1946.

38: 0.4tatitsch. K. 'Intermediate Ballistics;" USAMC Translation.FSTC 381-T65-3iZ. October 1965.

39. Petersen. H. L. . Encvclpedia of Firearms; New York: E. P.Dutton & Co. , Inc.; pp Z99-303, 1966.

40. Pous. L. C. W., "So.,nd Me& .rement on Small Arms I;" Instituutvoor Zintuilgfysiokogie Rve-Tno (AD 811 290). Netherland, !q66.

41. Prandl. L. . and 0. G. Tietjens. Hydro- and Aero-Mechamcs;New York: Dover Publications. Inc. ; 1957.

42. Rdiner. G., Wave Diagrams for Non-Stead7 Flow in Ducts;NewYork: D. VanNnstrand, Inc.: 1955.

43. Salsbury, M., 'Effects of a Muzzl.i Brake's Diameter and Lengthon Overpressure and Efficiency;" U.S. Army Weapons Command.Rock Island Arsenal, Technical Report 66-2920 (AD 803 417).October 1966.

44. Schlenker, G. . "Theoretical Study of the Blast Field of Artilleryw•ith Muzzle Brakes:" Rock usland Arsenal, Report No. 6Z-4257(AD Z96 587), December 1962.

45. Schlenker, G,. "Contribution to the Analysis of Muzzle BrakeDesign•;" Rock Island Ardenal, Report No. 62-1794 (AD 276 154)May 196Z.

46. Skochko, L. . "Sound Analysis of Ballistic Shock Waves" (UL);Frankford Arsenal, Report R-1798. January 1966. (Confidential)

47. Skochko, L. . and H. Greveris, "A Source of Small Arm MuzzleNoise" (U); Fr-nkford Arsenal Peport R 1860, August 1967

(Conlidential)

196

49. Smith, F., ,Model Experimenks on Muzzle Brakes:" RoyalArmament Research & Development Establishment. RARDERepuwt 2/66 (AD 487 1Z1), February 1966.

49. Sonier, A. J. . "EvOauAtion of Gun, Submachine, 9 mm (ModifiedU.S. Caliber . 45 SMG, M3AI), with Silencer Attachment, NorthVietnam (Viet Cong)" (U); Springfield Armory. Report MR 8-1131,January 1965. (Confidential)

50. Sterett, L.S. , "Si'encere,' Gun Digest. 18th ED. . pp 135-138,(1964).

51. Waitng, W. . "Acoustical and Visual Attenuation Through DynamicRegualtion of Muzzle Gas Flow:" Springfield Armory. ReportSA-TR3-1911 (AD 634 649), June 196b.

197

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FRAN'~FORD 6REA 1117FRAN'FOR D A RSENAL UNCLASSIFIED

Philadelphia, Pa. 19137 W GROW$-

SILENCERS

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Technical Research ReportSa- AUTMO"04(D'ek d. M . ai* 80@f. betS)

LEýNARD W. SKOCHKOHARRY A. GREVERIS

4. NlPORT ATK M41. TOTAL "o• AOES ". VO. ot pari

AUGUST 1968 209 19 519 4" C•MTRACT OOR GRANT NO. 0. OIII1T@WS N5901¶T guObN'S "Sl

AMCMS Code 5542. 12. 46801.02*** ROJET NO ,R-1896

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of. 04161`011"IrON 9VA1MCWNT

- This document may be further distributed by any holder only wi•t•ih specific prior ap-

proval of the Cormnmanding Officer, Frankford Arsenal, Philadelphia, Pa., Attn:SMUFA J8100.

by. huPPLff..L£lNYART'+ 14015 [a.h II~~llONIQ lkCl MIaL.IAYA•'r C T1'%(TV

ASAWECOM

I&. £61 ftRCT

This report presents physicai and functional dercriptions and acoustical

evaluation of various domestic and foreign silencero aand silenced small armsweapons, Included are cross-sectional drawinigs and external view photographs

of all systems tested. An acoustical evaluation of each system is given in the

form of far field sound pressure-tir; e records. All major constituents of sound

signatures are iderntified and time-correlated with their respective sorces in

the system. Additionallv, the report preserts a record of silencing principles and

a theoretical analysis of the various noise generating phenomenon.

DD ,v. 147 73 ,•-: , , ' UNCLASSIFIED

LINK A L INK a L;N ca P. kt, II vY OLG w wT C,

Silencod Weapo nsSrnall Arrms NoisePreea~ure-Time Soatnd Records~Scope Troces

i ~Noise Source

Sound Pregsswre LevelzNoise Attenuation

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