Barrel too small for 1/2" threadding?

Discussion in 'Gunsmithing' started by cohunt, Aug 25, 2019.


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  1. cohunt

    cohunt Well-Known Member

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    Muzzle is .555"--- is this too small for 1/2×28 threadding? Not much left for a shoulder.
     
  2. Kimber7man

    Kimber7man Well-Known Member LRH Team Member

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    Looking at TBAC sheet they require a min 0.600” barrel diameter for 1/2x28
     
  3. cohunt

    cohunt Well-Known Member

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    I'm not mounting a suppressor to this rifle, just a muzzle brake-- sometimes that matters
     
  4. jmcmath

    jmcmath Well-Known Member

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    Eeek that’s not much. Kimber threads 7/16. On their pencil barrels that might work
     
  5. shortgrass

    shortgrass Well-Known Member

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    what's the bore of your rifle?
     
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  6. cohunt

    cohunt Well-Known Member

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    I know, I'm trying to stay away from 7/16 if I can
     
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  7. TwoMore

    TwoMore Well-Known Member LRH Team Member

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    I saw where Alex Wheeler used the muzzle for the buttress on a brake, and it was very cool
     
    Last edited: Aug 29, 2019
  8. J E Custom

    J E Custom Well-Known Member

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    That's enough as long as the bore diameter is small enough to leave .150 barrel wall on each side. The brake can be built to seat against the muzzle
    to get the same results.

    If the caliber is .224 you will be Ok, it needs a barrel diameter of .563 and you are just below the minimum with a 1/2" thread. if you go to a 32 TPI Pitch thread It will help.

    J E CUSTOM
     
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  9. jrock

    jrock Well-Known Member

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    tag
     
  10. cohunt

    cohunt Well-Known Member

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    yea, we have spoke about the min barrel wall thickness before-- this seems like its a preference thing depending on who you have thread the barrel or the barrel manufacture--I know it has been proven that too thin of a barrel wall does in fact cause muzzle swelling, but how much does it actually affect accuracy? Kimber threads their 300wsm and wm mountain ascent barrels with 7/16" threads, also many well known "recommended" gun smiths that build custom rifles will thread 30 cal pencil barrels in 7/16" also--- I agree with you that thicker is better and its better to err on the side of caution than go too thin, but I have seen 1/2 moa 30 cal rifles threaded 7/16 before and I have never seen about any safety issues so I guess if it comes to bench rest rifles then go for the thicker barrel wall, but for some lightweight hunting rifles it can work just fine to have thinner walls.
     
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  11. DSheetz

    DSheetz Well-Known Member

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    One of the reasons you have specs on how thin the wall thickness should be for threading is so that you don't have the threads cut through or cause metal to be pushed into the bore . I have seen where people ended up with what looked like a heli-coil thread repair coils after cutting threads you need enough meat left that isn't weakened to withstand the pressures that it will experience and not cause the bore to be restricted . I'm an old millwright not a gun smith or gun builder and have seen some things that will make you scratch your head or jaw drop in my life . I have just smiled shook my head and walked away on more then one occasion when people were doing something that they would learn by but not get hurt or hurt someone else . Just me .
     
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  12. J E Custom

    J E Custom Well-Known Member

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    Yes I hear you, but there are a lot of things that are marginal and some get away with them. (Some don't). I have also seen muzzle brakes shot off, barrels split and accuracy go bad because of thread pressure and poor thread fit. So when barrel makers tell me they won't flute anything that will end up less that .137 wall because of the many different conditions placed on barrels, I start with a minimum of.150 thickness to allow for thread fit and some of the other problems that are encountered .

    With certain low intensity cartridges a little less wan thickness can be tolerated. The reason that most 308 ARs are now threaded with 5/8 x 24 tpi threads was/is the failures of those with 1/2 x 28 TPI.

    With the proper barrel wall thickness the thread fit and bore compression can be minimized or eliminated and the risk of shooting the brake off is also eliminated. I have also seen muzzle brakes shot in half because the bore of the brake was to small for the bullet to pass through and the bullet took the end of the brake off. (But because of proper sized threads the rest of the brake stayed intact and no harm came to the shooter.

    So in my opinion, one might get away with cutting corners, but why risk it just because someone else did.

    J E CUSTOM
     
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  13. cohunt

    cohunt Well-Known Member

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    I agree, just seems odd that kimber would chance a 7/16" thread with 308 magnum calibers-- I can maybe understand 308 or 30-06 but wsm and wm seem like they are pushing liability problems In a world of attorneys
     
  14. J E Custom

    J E Custom Well-Known Member

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    I truly don't understand the use of threads with that little amount of barrel tenon.

    If you thread a 308 bore with a 7/16 thread diameter you will end up with a barrel wall thickness of between .045 thousandths and .050 thousandths at the minor diameter. and with the tops of the threads having a little flat (Like they are supposed to) you will end up with 80 to 85% thread engagement Max. 1/16 of an inch is .0625, so the barrel wall would be less than 1/16th thick. and if it were dropped, the barrel tenon could be bent or worse broken off.

    They are relying on the muzzle brake for strength and in my opinion that is not a good idea because it rely's on to many factors that can cause catastrophic failures.

    I can only recommend the way to do things and hope that it saves someone from from a failure or worse.

    J E CUSTOM