Accuracydegradationfrommuzzlebrakeerosion. ByJimSee

Occasionallyourprecisionboltactionriflemaystarttohavesuddenunexplainedaccuracyissues.Oftenoverlookedaretheerosionforcesonthemuzzlebrakewhichcancausethebulletclearanceholesto“tighten”.Wehaveallseencarbonbuildupinourmuzzledeviceandthisabsolutelywillcauseaccuracyloss.Butifthataccuracylossremainsafteragoodcarbonremovalcleaningweneedtolookdeeper.

Ifirstencounteredthisin2008,whenanewcustomersentinaspecialtypistolin6.5x284.After200roundshisgroupshadopenedupwelloveraninchandhewasrequestingmetofixtheissue.Afteraquickinspectionofactionscrews,ringsandbases,andaborescopebarrelinspection,Iturnedmyattentiontothemuzzlebrake.

Clearanceholesthroughmuzzledevicesshouldbeatleast.020”overthebulletsdiameter,sowithafewpingaugesIattemptedtomeasuretheholes.Thisparticularbrakehadlessthan.005”bulletclearance.UponcloserinspectionIcouldseethatthebrakewasopenedup.025”overbullet.Buttheeffectsofgasandpowderblastonthebafflesurfaceshadcreatedaburontheleadingedgeofeachclearancehole.Thatbursubsequentlyrolledintotheleadingedgeofthethruholecausingareductioninclearance.

Theendresultwasabulletthatwasbeingadverselyaffectedassoonasitleftthemuzzle.Myinspectionalsorevealedthattheoriginalgunsmithusedabrakethatwasofstainlesssteelofanon-heattreatedvarietythatwassofterthanbarrelsteel.Mylatertestingrevealedthatharderbrakestendtotakelongerfortheerosiontooccurtoapointthataccuracyisaffected.Ihavealsolearnedthrutheinspectionandconstructionofthousandsofriflesandmuzzlebrakesthatgreatererosionoccursbasedontheseotherfactors;shortbarrels,slowburningpowders,andlargecapacitycases(whichuseslowburningpowder)alltendtoincreasetheerosionfactor.

Thesolution;

Wellreallythatstartsduringthebrakesmanufacturingandinstallation.Sincethatveryfirstrevelationofthruholetightening,IhavesoughttocombattheoccurrencesandwhatIlearnedinbuildingmuzzlebrakesandtestingprocesseshaspaidoff.

NowIboreallmymuzzlebrakesto.030”overbulletdiameterduringinstallation.Thishelpsslightlybuttherealkeyistochamfertheleadingedgeofeachbafflesclearanceholewitha45degreechamferforabout.015ofaninch.Toproperlyexplainthelocationofthischamferpictureeachbafflethatthebulletpassesthruasasmallfunnel,Iamremovingthematerialthatcreatesthebur.Whenthebaffleisaperfectlyflatsurfacethematerialaroundtheclearanceholegetspoundedbypressureandcarbonresidue,thusitdeformsatthe90degreeedgeandflowsintotheareaofbulletclearance.Bycuttingthisverysmall“funnel”thematerialdoesnotgeta90degreeimpact,thusitismuchmoreresilienttodeformation.

Theprocessofchamferingthebaffleholesisaccomplishedrightafterbrakeinstallwhentheclearanceholeisbeingboredtoitsfinaldimension.IsimplywalkmyHSSboringbartotheleadingedgeofeachholeandcutthecorrectchamferwiththeanglethatisgroundonthecuttingsurfaceofthetool.Donethiswaymostbrakesthatareof28rockwellhardnesswilllastthelifeoftheriflebarrel,andlonger,withnoissuesrelatedtoclearanceholeerosion/burrcreation.

Repairofanalreadydamagedmuzzlebrakebytheuser;

Thisisrelativelysimple,slideapop-sicklestickinthefirstportofthebrakeclosesttothemuzzleorremovethebrakefromtherifle.Theintentistosimplyprotecttherifleboreandcrownfromtheprocessofde-burringtheclearanceholes.

Itakea¼”brassrodwithaslitinittoholdasmallwrapofsome320gritemerycloth.Ithenchuckthebrassrodinthedrillandhoneouttheclearanceholes,whichintheprocesswillfractureoffallthebursandgetyoubacktoyouroriginalclearancedimensions.Thisprocessmayhavetoberepeatedduringthelifeoftherifledependingonbarrellengthandpowderburnrateect.ThatIoutlinedabove.

Sorememberthesetipsifyou’rehavinganunexplainedaccuracylossthatyoucannotcontributetootheraccuracygremlins.