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Author Topic: Primer cause.  (Read 3952 times)

StevenTing

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Primer cause.
« on: January 17, 2014, 08:30:44 pm »
Anyone know what could cause the primer on the right? 

This is for a friend. 

This was in my AI today. It is the same load that I've been shooting - I have over 350 rounds with this load prior to today. Previously, absolutely zero pressure signs. None of the other cases that I shot today (other the ones with the popped primes) have any pressure signs.

Like 4 of them had the primer hole completely popped out (like the right one). And 6 or 7 more had the primer popped, but the piece was still intact (like the middle one)

Everything is the same. Same lot of powder, same lot of bullet, same lot of primers, same loading equipment, same dope pulling the handle on my press, same everything...

Brass is the same stuff I've been running for a bit now. This is 1x fired FGMM 308 necked down to 260.
Utah

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    JesseL

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    Re: Primer cause.
    « Reply #1 on: January 17, 2014, 09:08:01 pm »
    Is that brass being neck turned after sizing down to .260?

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    scarville

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    Re: Primer cause.
    « Reply #2 on: January 17, 2014, 09:49:17 pm »
    If it was pressure I'd expect to see some soot around the hole in the rightmost primer.  Was this a manual action or an auto-loader?  I saw some pierced and bulged primers in an AR-10 when the bolt unlocked before the case let go of the chamber.  Once the action was "timed" the problem went away. Or so I was told by the owner.

    It could also just be a few soft primers in the batch but again I'd expect to see some soot.
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    Re: Primer cause.
    « Reply #3 on: January 17, 2014, 10:09:11 pm »
    I'm kind of wondering if maybe the rifle isn't getting enough firing pin protrusion.

    Usually I'd expect that to cause light strikes, but maybe with soft enough primers it would still fire but allow the prime to extrude into the firing pin channel?

    I'd strip the bolt and see of there's any crud limiting the travel of the striker.

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    StevenTing

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    Re: Primer cause.
    « Reply #4 on: January 17, 2014, 10:22:55 pm »
    Well.  It is a bolt gun.  These are from a guy that does long range target shooting.  Other than that I don't know.  Figured this would be a good exercise as I've never heard of bulged primers or even the primer getting cut. 

    But what was interesting is that it was the same load, same powder, same primer, all from the same lots. 
    Utah

    coelacanth

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    Re: Primer cause.
    « Reply #5 on: January 17, 2014, 11:52:04 pm »
    I've not seen a case that looked like the one with the hole but I was also thinking bullet tension or maybe COL a little long and maybe in contact with the rifling at the moment of firing.  Sometimes there is enough variation in chamber dimensions even with the same caliber to cause that situation.
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    Mississippi556

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    Re: Primer cause.
    « Reply #6 on: January 18, 2014, 12:04:16 am »
    Same thinking here.  COL issue, trim length?  No signs of excessive pressure on the case head otherwise.  Mic the case just above the head on the blown primer cases and compare to the others.  Puzzling.
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    only1asterisk

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    Re: Primer cause.
    « Reply #7 on: January 18, 2014, 10:27:00 am »
    u
    I'm kind of wondering if maybe the rifle isn't getting enough firing pin protrusion.

    Usually I'd expect that to cause light strikes, but maybe with soft enough primers it would still fire but allow the prime to extrude into the firing pin channel?

    I'd strip the bolt and see of there's any crud limiting the travel of the striker.

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    While the bolt is apart examine the firing pin for damage. 

    mattitude

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    Re: Primer cause.
    « Reply #8 on: January 18, 2014, 11:07:12 pm »
    +1 on checking the firing pin but also look at the firing pin hole on the bolt face.  It's possible that the hole is enlarged from dry firing (usually caused by the taper in the firing pin) and that can cause that cookie cutter like hole in the primer.
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    only1asterisk

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    Re: Primer cause.
    « Reply #9 on: January 19, 2014, 12:11:45 am »
    +1 on checking the firing pin but also look at the firing pin hole on the bolt face.  It's possible that the hole is enlarged from dry firing (usually caused by the taper in the firing pin) and that can cause that cookie cutter like hole in the primer.

    oversized firing pin holes are standard out the box on some guns these days.  It is the most likely cause,  but all bases should be covered esp if this rifle has never experienced this before.

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