Factory Ammo Pierced Primer

Discussion in 'General Discussion' started by Brown Dog, Aug 6, 2007.

  1. Brown Dog

    Brown Dog Writers Guild

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    Took part in sporting rifle competition on Sunday, 100 and 200m, 40 shots at a variety of animal targets, all shots sitting with sticks.

    I was unable to shoot at 3 target exposures due to sorting out a failure to fire.

    The failure to fire followed a pierced primer (see pic).

    Testament to the AW that, after a bit of bolt jiggling (but not stripping) it continued to fire....despite having a piece of brass inside the bolt assembly (see pic of what came out when I stripped the bolt yesterday evening).

    Not sure what to put this one down to.....a brittle primer?

    [​IMG]
    [​IMG]
     
  2. BountyHunter

    BountyHunter Writers Guild

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    What action?

    What caliber?

    What Primer?

    Factory or reloads?

    BH
     

  3. Brown Dog

    Brown Dog Writers Guild

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    AW ( = Accuracy International, Arctic Warfare)

    308 (there's a bit of a clue on the case heads in the pic :) )

    Post titled ' Factory Ammo Pierced Primer'

    (but to answer your question more fully: Sellier and Bellot Factory Match (launching 168 SMK) ) :) :)



    ....doesn't look like a high pressure issue to me...no gas fouling of the bolt...not seen anything like this before. As I said earlier, not sure what to put this one down to.....a brittle primer?
     
    Last edited: Aug 6, 2007
  4. BountyHunter

    BountyHunter Writers Guild

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    PICs will not open for me.

    sounds like either the ammo was loaded hot and might have soft cup primer and/or you have an issue with the firing pin length and or firing pin hole diameter.

    If it does it with other ammo, then you more than likely will have to have the firing pin protusion measured and maybe the firing pin hole bushed.

    Get a smith to check the firing pin.

    BH
     
  5. davewilson

    davewilson Well-Known Member

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    i agree with too much clearance on the firing pin and bolt hole.
     
  6. HeskethPritchard

    HeskethPritchard Well-Known Member

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    Me being a mere mortal with very little "gunsmithing" experience would someone please explain to me why the firing pin hole diameter could cause such a failure? I am not trying to be arguementative, far from it, I just don't understand the physics of it and why it would cause a hole in the primer cup. I understand the issue about the firing pin length just not why the FP hole diameter is important.
     
  7. HeskethPritchard

    HeskethPritchard Well-Known Member

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    DaveWilson

    Can you help me in my quest for knowledge on this one????
     
  8. CatShooter

    CatShooter Well-Known Member

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    Contrary to some of the "guesses"... it is clearly NOT an oversized pin hole.

    With an oversized firing pin hole, you get cratering with rounded edges on the outside of the crater, even on light loads. There is no (as in ZERO) cratering on the case that did not perforate... there is nothing wrong with the firing pin hole. The pin to hole fit is fine.

    Both primers look flatter than that usually seen with factory ammo, that might be the first clue. Keep in mind that S&B, and other European ammo makers, load to a higher standard (CIP), instead of the US standard (SAAMI). There is 5 to 10 Kpsia difference. Not dangerous, but it does add to the pot

    The flattening could be due to a maximum chamber and minimum case, as a flattened outside primer edge is common with Max chamber and Min case.

    But when primers perforate like that, it is because the pressure was so high, that it pushed the pin WAY back into the bolt, far enough so that the plug from the primer was inside the bolt... that is HIGH PRESSURE.

    This type of perforation can happen if the firing pin spring is weak. (I had this happen a few weeks ago in a Rem 40XBBR, and replaced the spring, and the problem stopped. It was 33 years old... ).

    But if you have no reason to suspect the spring, and considering that the primers are flattened, I would suspect that the S&B ammo is giving you more pressure than you want.
    I would try some other brand of plain vanilla load, like Fed GM Match, or Rem or Win hunting ammo if you have some lying around.

    .
     
    Last edited: Aug 23, 2007
  9. HeskethPritchard

    HeskethPritchard Well-Known Member

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    Wow

    That is worrying. Brown Dog is a buddy of mine, he lost the comp to me on a technicality and I'm sure when he gets back from his leave he will tell all about how I won :).

    I will make sure he reads the posts. I know his rifle isn't that old but you never know I will get him to check it.

    Catshooter thanks for the advice but one more question if I may, some of the guys have mentioned an oversize FPin hole and I (and I am pretty sure Brown Dog hasn't either) haven't any experience of this phenomama what are the signs/symptoms? what do we need to look for?

    For the avoidance of doubt, I do not think your advice wrong just curious to expand my knowledge and as others have mentioned it it must happen.
    Thanks in advance

    HP
     
  10. CatShooter

    CatShooter Well-Known Member

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    Symptoms of an oversized firing pin hole are easy to spot.

    With light loads, or plain vanilla loads, you get cratering, but no other signs of pressure... the outer edges of the primers look normal and rounded, and the edge of the primer dent looks "soft", that is it's rounded, and not sharp like the edge in the photo of the case you have in your post (the one not perforated). The cratering looks different from that of heavy loads.

    With heavy loads, the cratering has a straight wall on the outside, sorta like you turned a shot glass upside down. That is because the pin is being pushed back by the pressure, and the primer metal follows the pin, and conforms to the straight wall of the firing pin hole. The edge is sharp, and feels sharp as you draw your finger across it.


    But with an oversized pin hole, the primer metal flows into the space around the pin because it is not supported.

    The "crater" has a soft/rounded look, like if you sliced a donut or bagel in half and lay the top half on the table.

    This donut or bagel look is the classic look of an oversized pin hole.

    (This can also happen with a firing pin hole that is proper, but beveled with a 45° countersink because the edges of the hole were burred from drilling too fast. In this case, the primer flows into the 45° countersunk space.)

    If you look at the fired case in your first post... not the one that is missing the middle, but the other one... it has a very sharp edge at the edge of the pin dent...
    ... It would be IMPOSSIBLE to have this sharp edge if the hole were oversized.

    Oversized firing pin holes are common with Remington rifles... so much so, that there is a cottage industry in the USA of gunsmiths that specialize in drilling the bolts out, putting bushings in them, and then re-drilling the bushing to the proper size.

    And, if suspected, it is easy to check... let the pin down, and look at the pin sticking out of the bolt face... there should be no more than a few thou (0.002" or 0.003") of clearance.

    I recently had two Remington XR-100 brought in, and both needed the bolts to be replaced or bushed and re-drilled because the holes were oversized.

    Hope this sheds some light on it.

    .
     
    Last edited: Aug 25, 2007
  11. specweldtom

    specweldtom Well-Known Member

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    There appears to me to be a raised,eccentric ridge around part of the perimeter of the firing pin strike on the left. Also, the little firing pin nose shaped piece that ended up inside the bolt appears to have been ripped out of the primer, not sheared out cleanly. Both pictures indicate more than optimum pin/hole clearance, and high pressure.

    I'm betting it'll happen again. Wear glasses.

    Good luck; let us know what you find. Tom
     
    Last edited: Aug 23, 2007
  12. HeskethPritchard

    HeskethPritchard Well-Known Member

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    Can't thank you enough Catshooter thats a real help. My buddy doesn't own a Remington but I do so I will keep an eye out for it.

    So your analysis points specifically at high pressure and not oversized FPin hole if I am understanding you correctly.

    Tom & Catshooter

    We will keep you posted, I dont know when Brown Dog is back but we'll report back and hopefully get some pickies of other loads for comparison.

    Thanks again

    HP
     
  13. CatShooter

    CatShooter Well-Known Member

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    Yes... there are two parts to it. The flattened primer (on the outside of the primer) and the punched out primer.

    These two signs together are pretty much definitive.

    If the primer was flat on the outside, and rounded on the pin indention, it is a sign of headspace (not necessarily TOO MUCH headspace).

    If it had a crater that was like the top of a donut or bagel, it is oversized firing pin hole.

    But there is one more thing. On the case that is NOT perforated, the firing pin dent in the left primer is shallow, and well defined. The typical pin dia is 0.055"... and the typical pin protrusion is (Ta, ta) 0.055"... so under normal conditions, the pin dent should be about as deep as it is wide. But in the left hand case, the pin hole looks to be about 1/2 as deep as it is wide... it has a dished shape. Buy itself, I would not say this is a definitive cause of anything... but taking in account all the other things, I would say this is further evidence of higher than acceptable pressure. And further, there is the slightest beginning of primer material starting to ooze (for lack of a more scientific word), as though with a little help, it too would perforate.

    Reading primers is a black art at best... taking years of looking at the little devils, and correlating what you see, with what you know from other sources (pressure gauges, etc).

    .
     
    Last edited: Aug 25, 2007
  14. CatShooter

    CatShooter Well-Known Member

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    They do not. If you had ever dealt with a rifle that had over sized firing pi hole, you would know it right away.

    These cases do NOT show any signs of oversized firing pin holes.

    .