Brass shavings in bolt

[Dave in NGA]

I'm not a 'black rifle' guy but I recently put an AR pistol together and after approximately 20 rounds it had a failure to chamber. Even the forward assist couldn't make it chamber a round. When I took it apart the bolt face was full of brass shavings. I suspect the problem maybe connected to the extractor. What do the experts think? I sure do need some help before I do something wrong and make matters worse.

TIA
Dave in NGA

[epa223]

By chance did you look at your fired casings? I'm thinking a sticky chamber may be causing the extractor to tear the "rim" of the casing slightly therefore making bits of brass shavings. I've never had this happen to me so it's just a guess.

[Litt'le Lee]

did you install the barrel to the receiver? and do you have a headspace gauge?? and are you using commerical or handloads ??

[barretcreek]

If you assembled the upper from parts did you have the correct gas tube and block? I think the whole gas assembly has to be the proper one for the length from the gas block to the bolt carrier to avoid getting too much pressure to the carrier.

[joem]

Many questions but little data to make a judgement call on the problem. Too many possibilities and everything is a WAG. Nice pics that would help.

[Dave in NGA]

The upper (with barrel mounted) was a purchase from 'Freedom Munition' (PSA?) and has a 10" barrel chambered for 300 AAC Blackout. Ammunition is a combination of sub and super sonic factory and hand loads. Same shaving issue with both loads. There are strong marks on the brass indicative of the extractor getting a 'bite' on the rim. The subsonic loads are light enough to extract but not eject. The supersonic loads function correctly, up till the jamming occurred. I'm guessing sharp edges on the extractor. The extractor, spring, pin, and doughnut look correct.

The 'rough chamber' idea is interesting and I will find someway to inspect. Being a 'new' assembly and first time fired, I'm hoping there is nothing wrong with the barrel, chamber, and gas system. The lower is a Spikes Tactical assembled from parts and functions OK. I guess I could try some factory loads in lighter bullet weights such as 110 or 125 grain. Still looking for ideas before changing anything.

Thanks guys for the ideas.

[RED]

Another WAG... Take a look at your magazines. Have they been modified to feed the larger diameter, 30 cal bullets? Are the necks of the cases being "shaved," as they leave the mag or as they are entering the chamber?

[Dave in NGA]

Red, you may have hit on it. I was using some old Colt 20 round magazines I had sitting on the bench. I've never used these mags before and maybe they are the root problem. I've heard the typical AR magazine can be used on the 300 Blackout without modification.

Thanks

[RED]

My 20 rounders have a 3/8" reinforcing strip inside the leading edge. Try relieving/chamfering that sharp edge and see what happens... maybe nothing but may end your problem.

[Indy]

I just had in a customer's AR and he had installed the mag release with a couple extra turns. The magazine could not be seated all the way in the mag well. The nose of the cartridges were push into the top of the mag well rather than the feed ramps. There are a lot of after market magazines with rough edges on the feed lips. I inspect them, and
pass a stone over them a few times. The stoning tends to eliminate many feed issues, and brass shavings.
Indy