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Posted: 10/9/2012 6:58:14 AM EDT
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So I posted this in trouble shooting, but got no dice.
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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Sorry to hear about your experience. I am by no means an expert, but have been doing a lot of reading about the 300 and can offer minor insight based on what I have read that corresponds to your info. Couple questions to help dial in the issue:
1 - what gas length is the new barrel? what weight/type buffer/spring? 2 - have you fired any other ammo than the UMC? 3 - did you save any fired brass to get a picture? Something to note is that the UMC is having a rather.... well... lukewarm reception to the market. Yes it is cheap, but there have been a lot of people having issues with it. Some have no issues at all, others have had massive accuracy issues, but dont recall any of the "leftovers" that you have had. I remember reading SOMETHING about those rings, but cant for the life of me remember what it related to. The depth of seating is something that has been a concern for a while with the UMC, but again some people have issues others do not. What I have taken away from it is that for better performance, repeatability, and quality of shooting you should change to a different company for ammo. Hornady seems to be the best of the 300 line, but its a bit of money. PNW arms seems to be ok and closer in cost to the UMC, Nosler, Cor-Bon, and sierra are other options for ammo that have gotten high marks. the gas system is different in the 300 than the 5.56. The new barrel, being 16", was probably a carbine length correct? the real question is what the gas port was drilled out to. I've seen 0.08-.125 depending on how they wanted to focus the direction of the rifle. larger hole, more gas. This is key for when going with a heavier bullet, meaning to cycle the the rifle with 220 subs without a suppressor you need the larger gas port, but 100-140 supers will be over gassed with the same setup to cycle 220 subs. So, I said all that to say this: you may need to change the buffer weight to work properly, or depending on the gas system in place, you may need to make other alterations. sadly I am not familiar enough with troubleshooting the 300 yet to help you dial it in, just what I know the issues are that have been presented when people change from a 5.56 to a 300BLK instead of a dedicated 300 build. Dunno the policy on advertising other sites, but there is another place that is dedicated to the 300 that may get you more direct help for your concerns. T |
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Quoted:
Sorry to hear about your experience. I am by no means an expert, but have been doing a lot of reading about the 300 and can offer minor insight based on what I have read that corresponds to your info. Couple questions to help dial in the issue: 1 - what gas length is the new barrel? what weight/type buffer/spring? 2 - have you fired any other ammo than the UMC? 3 - did you save any fired brass to get a picture? Something to note is that the UMC is having a rather.... well... lukewarm reception to the market. Yes it is cheap, but there have been a lot of people having issues with it. Some have no issues at all, others have had massive accuracy issues, but dont recall any of the "leftovers" that you have had. I remember reading SOMETHING about those rings, but cant for the life of me remember what it related to. The depth of seating is something that has been a concern for a while with the UMC, but again some people have issues others do not. What I have taken away from it is that for better performance, repeatability, and quality of shooting you should change to a different company for ammo. Hornady seems to be the best of the 300 line, but its a bit of money. PNW arms seems to be ok and closer in cost to the UMC, Nosler, Cor-Bon, and sierra are other options for ammo that have gotten high marks. the gas system is different in the 300 than the 5.56. The new barrel, being 16", was probably a carbine length correct? the real question is what the gas port was drilled out to. I've seen 0.08-.125 depending on how they wanted to focus the direction of the rifle. larger hole, more gas. This is key for when going with a heavier bullet, meaning to cycle the the rifle with 220 subs without a suppressor you need the larger gas port, but 100-140 supers will be over gassed with the same setup to cycle 220 subs. So, I said all that to say this: you may need to change the buffer weight to work properly, or depending on the gas system in place, you may need to make other alterations. sadly I am not familiar enough with troubleshooting the 300 yet to help you dial it in, just what I know the issues are that have been presented when people change from a 5.56 to a 300BLK instead of a dedicated 300 build. Dunno the policy on advertising other sites, but there is another place that is dedicated to the 300 that may get you more direct help for your concerns. T The gas system is carbine, standard CAR buffer, the spring is one I've been using for several years buy has probably not seen more than 1k rounds. I did not fire any other ammo, the UMC is all we had where I work and get a discount so that's all I had for now. I've got all the brass except for a few pieces we couldn't find. I're been reading some on the other site of which you speak. I believe that is where I found the oring fix to help with extraction. That part doesn't bother me so much as the "leftovers" in and around the chamber. I may join up over there and see what they say. |
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I recall seeing a thread about this over on 300blktalk.com. It was an AAC barrel and I think that the chamber was too tight or unfinished and was shaving copper off the projectile.
Here is the thread over there Copper Rings And here are pics of the copper ring. 
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Quoted:
I recall seeing a thread about this over on 300blktalk.com. It was an AAC barrel and I think that the chamber was too tight or unfinished and was shaving copper off the projectile. Here is the thread over there Copper Rings And here are pics of the copper ring. http://img.photobucket.com/albums/v221/tokarev/Ruger%20SR556%2068%20SPC/103_0149.jpg http://i.imgur.com/5w7sE.jpg This appears to be the issue. Looks like I'll be contacting CMMG. |
| Well, after contacting CMMG, they're issuing me a return label to send the barrel in. Someone had asked the gas port size, since I had to disassemble the upper, I went ahead and measured it and got .110-.112. My calipers are cheap and it kept jumping back and forth. I'll update when I get it back. |
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WOW! That is crazy. 
You would think barrels would be reamed properly, especially in the case of it in the AAC barrel. From what I read, it is not an AAC barrel, it is from another manufacturer. The post on 300blktalk was about an AAC upper having the issue, also the above picture is from that thread and was a 6.8spc having the same issue. |
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Quoted:
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WOW! That is crazy.
You would think barrels would be reamed properly, especially in the case of it in the AAC barrel. From what I read, it is not an AAC barrel, it is from another manufacturer. I think he was talking about the thread linked to on 300blktalk. They were AAC barrels. |
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Quoted: Quoted: Hmmm I just found one from my new Noveske barrel... no function issues so far though. What ammo? Remington UMC 115grn CTFBs The upper has about 300 rounds through it and this the first one I've seen. luckily I saw your thread the other day, so came in to find out more. Edit: Just re-read your first post same ammo obviously... Guess I'll have to mail order some stuff as these and the 220's are the ONLY loaded ammo I can find locally! |
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