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Thread: gap semi 308 piercing primers

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    gap semi 308 piercing primers

    Took my gap semi 308 ar out to sniper qualification and began to have issues. It's a 18" barrel which I always run supressed (.308 surefire 762ss can) with an adjustable gas block and hyd buffer. It began piercing primers on me with factory Hornaday tap match ammo. About 30% looked normal, 30 % deeper than normal indents, and 30% actually had a hole through the primer and the pin punched out a nice disk piece of metal.

    The gun does need to be cleaned, and it began to have a few chambering issues as well near the end (of course there could be metal fragments in the chamber now). My question is if the pierced primers could be related to the dirty chamber, or is it the ammo, or maybe a too far protruding firing pin is the suspect I should check? I didn't notice any other signs of high pressure.

    I have not noticed this before with any ammo (but this is a new case), rifle has about 2500 rounds through it. My plan is to clean it real well and run to the range tomorrow before work, try the tap again, and also some Fed GMM I have. If both ammo types still show piercing the primers in a clean rifle, I guess I should change out the firing pin?
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    Re: gap semi 308 piercing primers

    Have you tried calling GAP and talking to them?

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    Re: gap semi 308 piercing primers

    I think you answered most of your own questions. The fact that it needs cleaning could cause a higher pressure in the chamber but it could also be a combination of many things to include the ammo itself. If you clean it and you still have issues then I would say give GAP a call.

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    Re: gap semi 308 piercing primers

    Hornady has been having issues with pierced primers in their Superformance offerings, maybe the issue had made it to their TAP as well.....



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    Re: gap semi 308 piercing primers

    Hornady has been having issues with pierced primers in their Superformance offerings


    has this been wide spread?

    been running it in my GAP Gladius

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    Re: gap semi 308 piercing primers

    Shot a couple back at the range before cleaning and the brass looked ok, but the rifle was cool. Cleaned it and it looks to be back to normal. Shot both fed and the hornaday match with no piercing, the fed primers do appear to be a bit harder. I am swapping out the firing pin because the tip looks a bit deformed, can't say it is a cause or the result of the issue. Will keep an eye on it, I'm guessing it was a combo of dirty gun with it getting warm from multiple rounds.
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    Re: gap semi 308 piercing primers

    I had this problem once, it turned out that the firing pin channel/recess at the bolt face was too large and did not support the primer properly. you will end up with primer frags either wrapped around the tip of your firing pin causing slam fires or bound up between the channel wall and the firing pin causing either a slam fire condition or a failure to fire. new firing pin, and new bolt is what you need.

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    Re: gap semi 308 piercing primers

    Primer piercing is mostly caused by oversized firing pin holes on the bolt face. The firing pin has little to do with it, but several pierced primers will destroy your firing pin as you observed: that is an effect, not a cause. You should measure the diameter of the firing pin hole on the bolt face with something accurate and report that back to GAP. You'll probably end up sending them the bolt if you want it fixed for good: bush the hole smaller or replace the bolt.

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    Re: gap semi 308 piercing primers

    *firing pin hole that is what i meant to say.

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    Re: gap semi 308 piercing primers

    Turn your gas block down when running suppressed....

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    Re: gap semi 308 piercing primers

    FWIW...
    I just ran a test on my DPMS due to primer piercing...

    All same brass/powder charge/bullet, with only different primers to see how the primers fared... (7-08 cartridge)

    Wolf and winchester primers were 10 for 10 , no piercings...
    with the edge going to winchester (less deformation of the primer)
    cci pierced all 10
    Fed GMM pierced 2 of 10

    BTW, this was with the minimum recommended powder charge

    Rifle was stripped/cleaned/lubed after every piercing in an attempt to reduce variables....YMMV...
    If freedom was free, why doesn't everyone have it?


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    Re: gap semi 308 piercing primers

    Originally Posted By: Scooter-PIE
    Primer piercing is mostly caused by oversized firing pin holes on the bolt face. The firing pin has little to do with it, but several pierced primers will destroy your firing pin as you observed: that is an effect, not a cause. You should measure the diameter of the firing pin hole on the bolt face with something accurate and report that back to GAP. You'll probably end up sending them the bolt if you want it fixed for good: bush the hole smaller or replace the bolt.


    This has been my experience too. Manufacturers really need to correct this defect of firing pin holes too large. And it is a defect!


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    Re: gap semi 308 piercing primers

    KYs got it. Get a Palladin 3 position block and itll fix it
    Originally Posted By: KYshooter338$
    Turn your gas block down when running suppressed....

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    Re: gap semi 308 piercing primers

    lol, I checked the adj gas block and had it in the unsupressed position [img]<>/blush.gif[/img] moved it back and runs fine.
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    Re: gap semi 308 piercing primers

    I had a rifle that was constantly punching holes in the primers, especially with CCI primers. Remington primers would get a nice big rim around it. This was at 4grains under max load by the books. As it turns out, by sheer coincidence, I accidentally broke the nice lil titanium firing pin when I was cleaning out the bolt from one of its excursions. needless to say I didn't have enough cash for another one so I got a plain jane standard weight stainless steel pin.

    Primer hole punch problem solved.

    Here's the logic: the firing pin doesn't have enough mass and momentum to maintian long enough contact with the primer to keep it from flowing back into the primer hole. Try adjusting your block or getting a heavier firing pin...or both.
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