My experience with seeing brass with the rim ripped off like that is it was hanging  up in the chamber.  What I always try first is to put a decent chamber brush in a hand drill. I then dip the brush in Hoppe's #9 and give her a light spin in the chamber. Sometimes they are just dirty. But, inspect closely as sometimes there can be rough machining marks in there and they can cause the case to hang up.

Good luck...

My DPMS was doing the same thing, till I polished the chamber a bit. 20 ga bore mop and flitz.

Every rifle manufacturer packs their products for storage, not for shooting.  Preservative oils don't lubricate properly for rifle operation, so you need to thoroughly clean a new rifle before you take it to the range.  VERY thoroughly.

I completely disagree with putting a chamber brush on a drill.  You don't need that, ever.  Using a chamber brush on a chamber rod] and turning it by hand is all you need.  Putting your brush on a drill gives you way too much speed and leverage, and that bronze can actually damage the chamber's finish.

Read my post again....A LIGHT SPIN....... Been shooting for 50 years and never hurt a firearm yet...but then I am very careful about what I do. I have fixed quite a few firearms with this simple procedures. Also, I use a light spin with a small drill motor for another reason....when you shoot for 50 years you probably have some arthritic hands to show for years of work.

I stand by what I said. Never seen it hurt anything when done properly.  But, you are allowed to disagree with anything I suggest.

Would imagine the machining in the chamber is rough, this is the most common problem.

Did you alter the gas port at all? The rim tear shows it is trying to extract but the brass is stuck in the chamber during extraction. This can be caused by to much gas and the case still under great pressure at the time of the attempted extraction. To much gas can cause this as well as from a out of spec chamber.

Sometime a new builder will increase the gas port size thinking they need more pressure to make it pull the case and this just makes it worse.

If you did not alter the gas port I am betting on the chamber or an improperly drilled gas port from the barrel maker.

If you have pin gauges (Or a number set of drills) you could check it to see what size it is by removing the gas block and seeing what the biggest size that will go in it.


I would also try and shoot some (Weak) military ball such as the Winchester white box 7.62 since it is milder than the high power (And higher gassing) ammo you are using.

Had the same problem. Armalite worked it over and runs fine now. Took about a month.

After you fire the case is expanding in the chamber.........so you have a tight chamber that may need polishing out.  Suggest  a chamber polishing brush. Just made of that. Same type of honing brush they use on car motor cylinders but made for weapon chambers. A small shotgun bore brush wrapped with fine steel wool and light abrasive cleaner and a drill will work in a pinch........info on you tube on procedures.

Flex Hone  is the name of the brush .........flex hone has a good website.

If you can eject it manual......then it's not a chamber problem.

You might be over gassing or too hot of handloads for a AR 10

U can slow the bolt down by installing a heavier buffer like H6 .      

I have a feeling that it's your loads your shooting not your gun ........AR 10  take a range of pressure to operate properly.

Good load for AR 10

IMR 4064 @ 41.75
175 Sierra MK
Fed 210 Match
FC gold Medal brass

"Done properly" is the problem.  With a drill most people overdo almost everything.  You may have a great technique, a light touch and an excellent track record, but Joe Thumbfingers won't.  On the other hand, you have to be very persistent to do anything bad with a chamber brush on a chamber rod, while a few spins with that setup will fix almost any "gunk in the chamber" problem without power tools.

No offense to you was meant.  I wasn't suggesting YOU were messing up your rifle.  I DID intend to make others think twice because your advice is almost certain to encourage more than a few people to go way too far.  "If I'm s'posed to use a drill, that must mean I press hard and swish it around a lot..."  A little information is dangerous in the hands of those with little experience..