Accuracy degradation from muzzle brake erosion. By Jim...
Transcript of Accuracy degradation from muzzle brake erosion. By Jim...
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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.
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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.