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Pressure Signs on Cases

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  • avvidclif

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    Here's a new one on me. I am familiar with the signs of excessive pressure when reloading but how about factory ammo?

    Here's the story: I have a DPMS AR I bought several years ago. It's been fired some but not a lot. Recently I started back shooting more and was shooting the DPMS with some reloads I had. I either bought them, doubt it, or loaded them years ago. They showed sign of high pressure, flattened primers, and some even fell out when ejected. This was on LC cases. It was also misfiring with light primer strikes. I put it up until I could clean the bolt and make sure everything was OK. It all checked out. The chamber was also cleaned at the same time (brush). Today I took it out again and was using Federal 55gr FMJ ammo bought at WM (100 pack). I happened to notice a couple of the cases had flattened primers (not as bad as the reloads) and one had backed out enough you could feel it. I can buy that with reloads that were a tad hot but not factory. That's something I've never seen and am at a loss for the problem. I talked to another LR shooter and he agreed it was high pressure but didn't have a clue why.

    Any ideas? It's shelved until I get this figured out.
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    Younggun

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    Could be that the throat was cut incorrectly and the bullets are jamming in to the lands. Should show a visible mark on the bullet if you cycle a round through without firing.
     

    benenglish

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    They showed sign of high pressure, flattened primers, ... It was also misfiring with light primer strikes. ... I happened to notice a couple of the cases had flattened primers (not as bad as the reloads) and one had backed out enough you could feel it.
    Just another data point - All those symptoms can be caused by excessive headspace. I have a 7.62x39 with all those problems due to an over-long chamber. Personally, I'd make use of a no-go gauge earlier rather than later in the diagnostic process.
     

    Dawico

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    Just another data point - All those symptoms can be caused by excessive headspace. I have a 7.62x39 with all those problems due to an over-long chamber. Personally, I'd make use of a no-go gauge earlier rather than later in the diagnostic process.
    Good point. Some measurements on fired cases may be useful information too.
     

    Bozz10mm

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    I agree. It sounds like excessive head space. You should check the headspace with a no go and a field gauge. My Bushmaster, when it was fairly new, was not showing signs of over pressure, but the bcg would close on a no go gauge, but not on a field gauge. If you can get the bolt carrier group to fully seat into battery with a no go gauge, it is not necessarily a dangerous situation, but if it seats on a field gauge...time to do something. A new bolt fixed the no go problem for me.

    The gauges are not cheap. A local gunsmith should be able to check the headspace for less than the cost of the gauges.
     

    benenglish

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    The gauges are not cheap. A local gunsmith should be able to check the headspace for less than the cost of the gauges.
    Too and sadly true.

    If headspace is the problem, though, the tab to the gunsmith is well worth it. It can save untold hours spent looking everywhere else for the problem.
     

    avvidclif

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    I want to thank everyone for their replies. Plenty of food for thought. I will first try and see if the throat has a problem by loading new ammo and looking closely at the bullets. That doesn't require anything but a little time. If no signs of contact I'll either buy the gauges (I'm a "use the proper tool" freak) or have a gunsmith check it out. I'll also mic a few of the fired cases with the flattened/ protruding primers. I'll let everyone know how it turns out. Any other ideas let me know.
     

    avvidclif

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    I took it to a local gunsmith. He polished the chamber and ran abt 60 rnds thru it without a problem. No signs of high pressure. Evidently there was a burr or something causing the problem. I'm going to pick it up today and will find out more.
     

    benenglish

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    A burr? I sincerely hope you do find out more. In fact, I'd be willing to pay that gunsmith an extra $20 to make me fully understand how "a burr" could cause all the symptoms you describe.

    I also hope he's not one of those "I fixed it; now get out of my shop" types who promises to educate you but somehow never manages to follow through. I've met way too many of those, unfortunately. At minimum, he should be able to tell you explicitly how the rifle acted when he used the headspace gauges.

    Looking forward to your post-gunsmith-discussion post to this thread.
     

    avvidclif

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    I can see it. A rough spot could cause seating problems and extraction. His first question when he called was to ask if it had steel cases fired in it, NO. He checked headspace and it was fine. Polished the chamber and ran 60 through it with no signs of pressure. He wasn't there when I picked it up so couldn't quiz him more. I'll run some thru it and if all is well go on down the road.
     

    benenglish

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    That's a better outcome than I would have expected. It's nice to see something work out for someone. My gun problems tend to be a little more complex so I'm a little envious... :)
     
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