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Thread: My first AR: 7.62x39 with Superlative Piston kit - Learning from failure...

  1. #51
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    Quote Originally Posted by Pressingonward View Post
    ...
    Out of the ~100 rounds I shot yesterday, I had one fail-to-fire on a brass cased PPU FMJ round. It has a tiny punch mark on the primer instead of the nice big dimple on all of the cases that fired correctly. I've read about light primer strikes, I'm guessing that's what this is? I don't quite understand how I could get such a tiny punch mark on this round - wouldn't the firing pin leave a big dimple whether or not the primer ignited?
    sometimes just the action of charging the round into battery leaves a tiny dimple, the AR-15 firing pin is free-floating in the bolt, inertia allows it to contact the primer going into battery.

  2. #52
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    My first AR: 7.62x39 with Superlative Piston kit - Learning from failure...

    Quote Originally Posted by Pressingonward View Post
    Out of the ~100 rounds I shot yesterday, I had one fail-to-fire on a brass cased PPU FMJ round. It has a tiny punch mark on the primer instead of the nice big dimple on all of the cases that fired correctly. I've read about light primer strikes, I'm guessing that's what this is? I don't quite understand how I could get such a tiny punch mark on this round - wouldn't the firing pin leave a big dimple whether or not the primer ignited?
    The combination of hard military primers and the spec for 7.62x39 has the primer seating recessed into the cartridge due to previous unintentional discharges during combat from bolts slamming home.

    Typically, due to the deviation from the 5.56 NATO AR bolt design, it either requires a specifically designed AR bolt face geometry for military 7.62x39 or a longer firing pin. The 7.62x39 bolt is usually 2x the cost so usually the longer pin is the solution.

    You definitely want to make sure you have one or the other for best ignition reliability. The Young bolt allows for standard AR firing pins because the bolt face is machined specifically for 7.62x39 specs.

    https://youngmanufacturing.net/produ...olt-7-62-x-39/
    Last edited by anarchocap; 01-11-21 at 07:32.

  3. #53
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    I have had very good luck with the RedX Arms enhanced firing pin. Only $11 shipped. http://www.redxarms.com/product-p/5061.htm

  4. #54
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    Quote Originally Posted by rpoL98 View Post
    sometimes just the action of charging the round into battery leaves a tiny dimple, the AR-15 firing pin is free-floating in the bolt, inertia allows it to contact the primer going into battery.
    It always dimples the primer. That's why you don't chamber a round in the house unless you have to. Rechambering the same round can get you an ND. Defective primer can go bang if it is too soft, or too high.

  5. #55
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    Quote Originally Posted by NQNPIII View Post
    It always dimples the primer. That's why you don't chamber a round in the house unless you have to. Rechambering the same round can get you an ND. Defective primer can go bang if it is too soft, or too high.
    From what I've read, this is extraordinarily rare. I think someone did an experiment and it took dozens and dozens of repetitions before a round actually went off, IIRC. Obviously, it's more likely with a soft or raised primer though.

  6. #56
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    Quote Originally Posted by NQNPIII View Post
    It always dimples the primer. That's why you don't chamber a round in the house unless you have to. Rechambering the same round can get you an ND. Defective primer can go bang if it is too soft, or too high.
    probably another reason the soviet, oh, excuse me, comblock, 7.62x39 uses the "hard" primers, that end up in us having to use an extended firing pin for AR-15 use.

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    I do think the dimple on the cartridge is probably from chambering the round. That leads me to believe that when I pulled the trigger the hammer didn't fall, or else there would be a bigger mark on the cartridge. I pulled the trigger twice to make sure I had pulled it completely. I don't remember whether or not I felt the hammer fall on the first pull - I certainly didn't on the second.

    Still not understanding exactly how this failure happened, but I'll pay more attention in the future to try and diagnose exactly what's wrong if it happens again.

    I'm running a Rubber City Armory BCG, and it came with a standard length firing pin with standard stickout. The primer on this round does not look deep-seated at all - it looks the same as all the other rounds. I do have a Red X Arms extended firing pin on hand, but will wait to use it until I convince myself it is necessary with the ammo I run.

  8. #58
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    Quote Originally Posted by georgeib View Post
    From what I've read, this is extraordinarily rare. I think someone did an experiment and it took dozens and dozens of repetitions before a round actually went off, IIRC. Obviously, it's more likely with a soft or raised primer though.
    I do know a member on this forum who is a LEO who fired a round through several walls and exited his house. On military bases you eject a chambered round into a barrel, or so I am told.

  9. #59
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    Quote Originally Posted by NQNPIII View Post
    I do know a member on this forum who is a LEO who fired a round through several walls and exited his house. On military bases you eject a chambered round into a barrel, or so I am told.
    Wow. That's actually why I always try to chamber while pointing in a safe direction. Old habit.
    “You have made us for yourself, O Lord, and our heart is restless until it rests in you.” -Augustine

  10. #60
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    Quote Originally Posted by NQNPIII View Post
    On military bases you eject a chambered round into a barrel, or so I am told.
    No, the clearing barrel is for dry-firing into, to prove that weapons are unloaded. Unlike cops, they generally aren’t trusted to go around with a loaded chamber all the time. Soldiers tend to re-chamber rounds like a bazillion times, entering and leaving “the wire”. The reason re-chambering is not recommended is that it desensitizes primers, although, I can’t recall ever personally seeing an issue. I do advocate rotating ammo, though. Its easy insurance.

    No offense to you or your buddy, but my first thought when someone has an unintentional discharge that was not visually observed, and they blame the gun, is that they are lying.
    RLTW

    Former Action Guy
    Disclosure: I am affiliated PRN with a tactical training center, but I speak only for myself. I have no idea what we sell, other than CLP and training. I receive no income from sale of hard goods.

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