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Thread: Firing pin leaves dimple on primer...

  1. #1
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    Firing pin leaves dimple on primer...

    I've noticed that when charging a round, the round shows the tiniest dimple on the primer from the firing pin. I'm running a DD barrel and DD BCG. I've had a few people who are better versed in ARs than me look at it and say it's a non issue, just rotate rounds.

    I was shooting a friends SA 1911 and he mentioned the titanium firing pin (9mm firing pin) to help prevent discharge due to light weight in the event of being dropped. Any chance a titanium pin in the AR will fix the dimpling?

    Even though I've been told it's not enough to make the round go off, it still doesn't feel right to me. I find myself slowing the charging handle. Last thing I need is a hole in my floor.

    Thoughts?

  2. #2
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    it's normal and every AR does that. if it makes you feel better, don't chamber the same round more over and over, but definitely don't slow or ride the charging handle.

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    Normal. Rotate the once-chambered round to the bottom of the mag. Chambering more than once can increase the chances of the primer not igniting.

    I keep track of how many times my .40 cal and 5.56 ammo has been chambered with marks from a Sharpie on the base of the case and never chamber either more than twice before shooting them.

  4. #4
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    Thanks guys.

    I'm curious as to why on the .40 cal?

    I rotate anyways, but because i got old Hornady .40 JHP that had the black powder coating, which gets chewed off when chambered. I've kinda ran out of rounds that aren't chewed up, so time to get new ammo. Curious on marking the .40 rounds also though....

  5. #5
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    I'm glad somebody else asked this question. I just noticed it the other night on the top couple of rounds in my AR magazine.

  6. #6
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    Like others have said, its normal because the firing pin is free to move. Also, as others have said, rotate rounds that have already been chambered to the bottom of the mag. Repeated chambering can ruin the primer and cause the round not to fire.

    I've seen a couple of different AARs where this happened in actual SWAT callouts. Not good. I believe Doc Roberts posted on another forum that it only takes something like 17 thousandths of an inch to make the primer unreliable. That number's from memory from awhile ago, so don't quote me or him on it though. Perhaps he will reply and give you the exact number. If not, I will see if I can dig it up for sure.

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    .40 cal pistol rounds are high-pressure rounds; kabooms are not uncommon when the same round is repeatedly chambered, causing bullet set-back and dramatically increasing the chamber pressure.

    It's a good idea to rotate your defensive ammo periodically anyway, and marking the rounds is a good reminder to do that.

  8. #8
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    Any chance a titanium pin in the AR will fix the dimpling?
    As discussed, the dimpling is normal. Titanium is great for some applications, but this is not one of them. The material is a bit more brittle and the FP tip more susceptible to chipping or erosion.

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    Quote Originally Posted by TriumphRat675 View Post
    .40 cal pistol rounds are high-pressure rounds; kabooms are not uncommon when the same round is repeatedly chambered, causing bullet set-back and dramatically increasing the chamber pressure.

    It's a good idea to rotate your defensive ammo periodically anyway, and marking the rounds is a good reminder to do that.
    Can we derail the thread and discuss this for a bit?
    How many times has bullet set-back been noted to have caused an AR kb?

  10. #10
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    The AR platform use's a floating firing pin like the M14 and alot of other military rifles.

    The military prepars for this but using primers with a thicker cup. Like the CCI #34 for 7.62 and #44 for the 5.56. They have to make ammo for use in machine guns with a much faster rate of fire so consider that as well.

    In 9 years in the military I have seen thousands of rounds chambered and the only ADs I ever saw where beacuse the solider had there finger on the trigger.

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