TW. ý'S. NAVAL PROVING GROUNDid

DAHLGREN, VA.

ri

i BXAXTINLTION OF GEP11al 20 MM AIRCRAFT MIUNITION

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i TE•CUTJCA LIBPARY T.copyC817~ih~LTO OF GlU20 't ASCRF ~i~U ITO

UNCLASSiFIE

NAVAL PROVING GROUITD

Dahilgren, Virginia

REPORT K0. 6-43

April 2. 1943.

E=4,j 1INATION OF GMIjdN 20 li;, AIRCRAFT LIý,,,ITIONr*

Naval Provin Ground Ca ptured Enemy E.uipment

Report No. 62

:. ~APPROVE): • . .m ZK•--

CAPTAn, U•.., .:INSPiETOR OF ORIMlCE IN C1L0_.

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PREFACE

iAUTHORIZAT ION

Specific directives for this investigation wereissued in Buoid ltr !l100 (Relb) dated Deceiaber 28, 1942.

OBJECT

To maize a complete physical, chetical and metal-lurgical study of two rounds of German 20m aiicraft aimuni-tion.

SMAIlVIkRy

rcosunlete exaaination has been sade of tworounds of German 20m ai craft Oerlikon amiunition.

These two iounds used steel cnrtridge oasestainufactured by deop draiyin, a apheroidized steel ofaeproximately SAE 1020 grade. A situdy has been .zde of :the haidness distribution .nd giierostruoture of theseoartridge cases. It is shovm tlhrt south-&uxnealinp has, beenused to obtain the distribution of physical pr'opertiesnecessary for pxoper obturation.

For clitaatio pioteotion the steel has been coatedSith a cleet lacquer; a mie-trertraent stLilci to Pcrke•iizi%has been used to provide a satisfactory bond to the steel,.

The pio jectileo of this ad•unitiofl possossedunusual features, one being thin ualled and havin&e1 hi ghi"ocpacity and the other beinu, of convewMonal EZV desiagn but'iavini a rotatiant band aade frox a sintered iroa powder' ..i:••• : oatiptot,.

11b ootaplete diawing has teen aiae ot the aW u-. .

tion h"av-ing the hihk capacity projeotije,. .

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I: CONTMTTS

Page

* I INTRODUCTIOTT ..............

II INVESTIGATI(M

(A) PHYSICAL **.'........... 2

(B) CBEIC.AL .. ... ........ 2

(C) l1i~TklLUIIGIC.AL ........ 2 - 4

Page ii" I

LIST OF VIQMS

OppositePage

"Fig. 1 - NPG Photo No. 626 (APL)Ammunition as received....

Fig. 2iL - NPG Photo No. 656 (APL)Acid etched cross-sectionof CItE 395 ....... . ... . ..... 2

Fig. 2B - ZIPOG Photo No. 657 (APL)Acid etched cross-sectionof GEE 394..... ... ......... 2

Fig. 3 - Photomicrographs of cartridge3

Fig. k Graph of hardness distributionof caitridge case.......... 3

Fig. 5 * Licrostructures of projectiles 4

Draing ITPG wvg. 103 (iPL) - Drawinqo' lound OLE 395........... Inside back

cover

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I ~ITTRODt3CTIOYIT

Two iou~nds of Germ~an 2Oi.im aircraft ammflunitionwere received on January 23, 1943, by the &ýi~aor andP:-ýoJectile Laboratory of the 1-aval Provinp, Ground ofDahl~r en, Virginia, for physical, cheiaical aind mietal-luxgical examination.

The ararauflition ias recovered. folloving thecrash of rA ('emin F~ocke-Wulf pxlane in Iceland onOctober 243 1942.

(s.) msio,- Fli(ure 1 s~ow thl s a,:jLunitiolI asxecuivod, u~`&e nd iiithout fuzes. Tb1 0 followin isa cuscriptiou of the chmactexistica, EL:!jeably andmnarkings ot this E,-±unition.

Run4 C22'ý95 - ýdiCra5ft Ooxr1i;.:n staiunitionusin- o st~eel curtridge case E.nd & thin w.al2.d hiejh

cuy.iit pojuotilo. Figure 2A. shois p ro jectil10and caitridge casuj in. cr'oss suction. Thu pý,oj~otilu hada totel (unfuzed) %auight of 40 grcams anId s"c. )&2& ity of.83 cu.in. Liu~ cartridgo oasc weighad 63 gra.iia *nd had

u capacity of 1.35 cu.in.

Thu pxo j o ti Iu ms !ctintod yiý-low iiith a bcch.oidO11t~fiC~ti1 ion lm aroulul thju iouthl; thoa I-10.ic coduwrs ý.tvmcillud In white at u!1poxi izu1,, iidbody:

ed g22141 as b 41 a41

Thý portion of tho moijocti1t. bulow thcý rotating ban~dwsluft unpuintod.

The cm-tridgto case vas a oat d wit.1i a c lteollofrquar and v~a idenitifiud by the followine baa 4uxkings:

IX 41 541 B "UJzA

4 fotaid UTZ, 14 - Airaraf t Corlikon ouiiwi-itionusig astoi'Cl Zt de ce. S StLiir to Caat of round 395

but with vi convwntiona. 1i OiT proj~oti1e with a self-~destruction fL-aturo. Soo, cross sootion. in Fieure 2B,

This proJectile bad a total unfuzed weight og85 ranm and a capacity of .192 ou'. in of HfL. and ,06

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V I9 290MiU ROMRAPIS AT VARIOU. 11STIONS

S ' Or A 20 W1 OS"' UA STML CAATMWZO CA.0%

plum 3.

Whe hardness distribution (plotted in Fig. 4)

shows that these cases have high physical properties, ten-sile and yield strength, along the center of the body and

06 around the rrimer podket resulting from cold work. Theseproperties gradually fall off towards the mouth reaching avalue almost as low as that of the original blanking asgiven by the head which suffered relatively slight coldworking.

Such a distribution of hardness is necessaryfor a cartridge case must have high elastic properties alongthe body for proper recovery, and a soft mouth and neak taperregion to permit proper obturation.

The h&rdness around the primer pocket is some-what higher than the hardness along the conter of the body.The deep etched structure of figures 2A and 2B show thatthis was obtained by a pocketing operation which cold-worked the metal; a fairly high hardness is desired at thispoint to prevent blowing out of the primer cup on firing.Such a method has evidently been successful for the primercup is retained solely by a three-point star-crimp. (3eeDwg. 103 (APL).)

The microstruoture of the head (See Fig. 3, Posi-tion A) can be considered identical to that of the originaldiso blanked from the strip. It shows partially spheroidized,elongated pearlitic patches in a matrix of equiaxed ferritegrains. This is the structure of a hot rolled plate. Themicrostructurea: positions B at the root and C and D alongthe body, show the same structure following progrossivelysevere cold working. * Position E at the mouth shows arecrystallized structure of small equiased ftaite grainsresulting from annealing; to affect such a recrystallizationof the cold worked grains the annealing must have beencarried out at temperatures between O000 F. and li000 F.

These cases hove a very good surface ap!peeranoe,being practically devoid of die marks; a oleaa- lacquer,soluble in alcohol and mineral acids and insoluble in water,canted the inside and outside surfaces. It aplpe.red that,this laoquer adhered well and would not chip off; however,its abrasion resistance appeared to be low - presumably itwas sufficient to tAthstand the abrasive action of the pro-i~ellant during transport.

Ithe steel had been pre-treated for lacquering'.by a surface treatment similar to 1,rkerizing. Such con-.ditioning is necessary for steel to provide a good bondingsurface for organic coatings' it is not in itself a protee-. .%ion a($ainst"cllmtie corrosion..

w g,. ao 500X.for A, B, .& Dgn~iotio foZtr SEtched-Vital

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Miorostruotue of iron rotatingband; showing a partially re-"P / '•' • ..... - crystallized matrix of ferritio"grains, with numerous and.inter-oonnsotio voids. Struoture of

JO a s9intered iron powder oompaot.$

S

SI 3VANIMIATION 200XETCHED NITAL

Mjorostruoture of high oapaoityProjeotile; showing a fine lamel-lar struoture obtained on fastoooling.

WAGNIFICATION 15001

STCH&D PIOPAL

5B

.Ed ,ostruotur6 of H.E... p-o..JAýOtiue; wowing naxrzltztd*~A• ureo of a e50 oarbo steel.

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uHictA Capacit Projectilc - The details of con-'Sstruction of thils projec'le-are given in KPG Dwg. 103(SXL);the novel body design permits an unusually high capacity ofbursting charge.

"Unlike the conventional 20Lim H.E. projectiles whichhave thick walls, are nmachined from plain carbon steel barstock and are not heat treated; this projectile is zade byhot drawing a chromium-molybdenum steel (see Table A) andthen oil quenching to produce a hardness of 38 - 40 1PC.

The microstructure (Fig. 5) shows a fine lamellar ostructure of carbidos and ferrite plates typical for thissteel composition when cooled fairly rapidly. It should benoted that there is no evidence of tempering. The hardnessobtained represents the maximum which a steel of such lowcarbon content can be expected to show without a drasticquench to form martunsite and then temp(ring. In applyingthe rotating band undex a banding-press, the thin wallpresents a special problem. This is solved by the use of aduraluminum supporting ring to strengthen the wall. Thefuze is retained to the projectile by means of a fuze adaptorwhich is punch-crimped in the projectile.

-H.ET. Projectile - The details of construction ofthis projectilc-a u fairly conventional; a cross section isshown in Fi&. 2B.

This projectile has bcon wachined from a lowchromium stuel bar stock (sce Table A); Fig. 5 shows thenormalized structure vihich is probably that of the oiiginalbar• stock; the haidnoss was 18 JR.

fairly The rotating band is unusual in that it is placedi fairly well forward on tho body (3/4 in, from tho base) andthat is wade from sintared iron powder. It appears thatneither the pressing nor the sintering of this powdered com-pact has been carried out to any great extent. Fig. 5 shows

the discontinuous nature of the bond which is tho result ofusing fairly low Iressuras in tho pressing operation. This'band is apperently coined slightly ovocsivz then sintered andfinally trussed onto the ;roJectile. TIe use of a suprortiaz-ring to plevunt .2 collapse of the wallv during this bandpressing, operati3n has beon discussed prfAviously.-

This band was found to be very friable, breaki.g-into i ny fu dLInts'vhilo being removed froju the projeotile.DBeoause of this brittleness, no reproducible hardness -10

*auasurceunt could be oaado.

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