copper residue on bolt....

[ARPILOT]

noticed a large amount of copper residue on the back end of my bolt....enough there that some got picked off with a dental pick.
this is a new pistol build (8.2" barrel 300BLK)
I expect carbon build up but not copper, never seen this on any of my other AR's
maybe this is expected on 300BLK "pistol" version ?? I know the gas port is large enough, maybe large enough to allow this ??

[Dr.Phil]

Your barrel likely has a rough gas port.
That is not out of the ordinary.
You can contact the barrel manufacture, polish your bore, or just shoot it until it wears down.
It shouldn't be an issue unless you see accuracy issues.

[rjacobs]

new upper. Might have a slight burr on the gas port. Keep shooting it and cleaning it.

I had a very high end barrel on my 223 SPR build that was throwing TONS of copper into the upper. After about 250-300 rounds it completely stopped. Consequently that was about the same time the barrel settled into a consistent 1/2-3/4 MOA barrel.

[dellet]

Keep in mind that you will need to check and clean your w/hole gas system, that way your next post won't be: "Trouble cycling subs"

[plant.one]

my CMMG had that problem - stainless barrel chipped a big burr when the gas port went through the lands and was shaving copper off the jacket of the rounds and into the gas system. (it must have been a single blade, everyone *KNOWS* multi blade razors dont shave hehe!)

i ended up with a complete stoppage - gun wouldnt manually cycle, gas port was blocked with copper flake, etc

called CMMG and they had me send it right in after seeing photo's.

give the mfg a call, send them photos and see what they have to say


you have a warranty (or should) - use it! you might be surprised just how eager they are to make a customer happy

[randyrucker]

These might solve the issue and help some with accuracy. I did one of my uppers with them.

http://www.midwayusa.com/product/847811 ... ubv1847811

[Alien]

I had the same problem while using Lil Gun powder.

My CMMG did not show anything on the bolt but typical stuff while I was using 300-mp.

First set of test loads with Lil Gun I started getting copper build up on bolt, I have some still welded on that will not come off without damaging it. Stopped using it and have not had anymore issues with copper being melted on the bolt.

Just sayin! In case you are using LG for you loads.

[ARPILOT]

Thank you gents for the info....nothing worse than a bur near my gas hole !
I'll shoot it some more and clean w/JB paste, we'll see if it goes away.

I wasn't feeling a bur during cleaning, pulled patch back and forth to see if it catches, but obviously it's got one.

[JJH]

Most likely your gas port happens to fall right on a land. Fire a couple hundred out of it and see if it clears up. I just did a 223 build this spring, and after the first 100 rounds I had a pretty good amount of copper on the back of the bolt. i took it p-dogging and put about 700 rounds downrange, and it is no longer building up.