Download - Accuracy degradation from muzzle brake erosion. By Jim Seeeliteaccuracy.com/services/pdf/2017/accuracy-degradation-in-your-rifle-system.pdfbrass rod in the drill and hone out the clearance

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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.

  • 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.