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Posted: 10/8/2012 8:32:35 PM EDT
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Ok, so last week I decided I wanted a 300 blackout upper, easy enough. Ordered a new CMMG 300 blackout barrel from Midway. Install goes well, gas tube lines up perfectly. Today, go to sight it in and run some rounds through it. Shoot 9 rounds flawlessly. Surprisingly, the scope is only a couple inches off at 100yds or so. Let my buddy get behind it to crank off a few. First round fires, doesn't fully extract, picks up another round and jams them both into the chamber. Get it cleared, next round chambers. I want to make sure that it didn't squib or anything. We drop the mag and eject the round. Here's where it gets funny. Around the bullet, closest to the brass are two copper rings (I will post pics of them). Never seen this before. But the bore is clear so we continue to try to shoot it, keeps doing the same thing. Several more of these copper rings fall out of the chamber area.
I've done some reading around on some different forums and have figured out that the extraction/feeding issue seems to be related to the extractor and whether or not it has an o-ring or not. I'm good with fixing that. However, the copper rings are just baffling to me. It seems as though they are from the jacket of bullet. But my question is what is making these almost perfect rings? The ammo used was Remington UMC 115gr and there weren't any signs of over pressure on any of the casings that I could see. Looking at the ammo, the bullets are greatly varied in how deep they are set in the casings. Some you can see almost the whole cannelure and some you can't see it all, and every where in between. I think I've covered everything, if not I can provide as much more info as possible to try to figure this out. There were more of these, but this is all we kept. They are obviously copper and seem to maybe have some lead attached to them or maybe just some burnt powder. I'ver never seen anything like it before. 
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| Bruce, I've already sent it off to CMMG. I wasn't getting many hits here, so i posted over in ar discussion and got a lot of responses. One pointed me to 300blktalk.com where someone was having the same issue with an aac barrel. Hers the link to my other thread.http://www.ar15.com/forums/t_3_118/587300_Problem_with_300_blackout_upper.html |
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Quoted:
Branden, Theory: Bullet inserted into case with a little shaved off the jacket causing a ring to form. This?... Have you closely examined a few of the rounds before you shoot them? You'll probably see the ring if its there. Maybe even be able to pick it off with your fingernail. Just a thought... |
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Quoted:
Quoted:
Branden, Theory: Bullet inserted into case with a little shaved off the jacket causing a ring to form. This?... Have you closely examined a few of the rounds before you shoot them? You'll probably see the ring if its there. Maybe even be able to pick it off with your fingernail. Just a thought... Nope, I try to inspect ammo fairly well before I load the magazines. If you click the link to 300blktalk in my other thread I linked to from AR Discussions, it shows a different manufacturers barrel having the same problem with 2 different types of ammo. |
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