I replaced my upper and my handguards the other day. I haven't had a chance to get out to test fire the gun. Right now I was just trying to cycle rounds through to see how it will feed. It feeds flawlessly from my two 20 round mags with the upper on both lowers. So far it has not fed for shit from 30rd mags. I've checked 5 mags that fed 100% before I changed the upper, Also it won't feed from any of those 5 mags with this upper and my other lower. The mags feed perfect with my other upper on either lower.

Another thing is thaqt when the rounds come out, ther is a scratch near the bullet tip in the jacket.

I gots not clue what anything could be. I really don't think it;s the mags. Or the lowers but one lower is a Oly PCR1 the other is an essential arms.

here's a pic of a couple of the bullets and the gouges in them


Here is a pick of how the round is getting hung up.

Just guessing here, but maybe a burred edge on the feed ramp?  


Hmmm...


-Hershey

Quoted: Just guessing here, but maybe a burred edge on the feed ramp?   Hmmm... -Hershey

It's the same barrel I had before, and this is the first time I've had a problem like this, that wasn't a loose carrier key, or mag related. I thought about that, but I don;t think it could be.

The receiver could be out of spec.  Deck height could be off and/or pivot and taledown holes too far aft or forward.

If you have a caliper, you could compare the working to the non working upper.

Quoted: Releasing the bolt from the bolt catch or wracking the charging handle? Fired it yet? Does any portion of the upper hang over the walls of the mag well?

I'll check when I get home. I planned on taking it out after work to test fire it. As far as bolt relese or wracking the charging handle. In the greatest of ARFCOM traditions, I've tried both, and with the same ending. Like I said, this is odd to me because 20rd mags feed just fine. It's only the 30's that are troublesome.  

Quoted: Yeah, that is the odd part. All are USGI?

Yes the 30's were two sanchez, two FN and one adventure line. the 20's were a colt and an adventure line.

Maybe I just gotta shoot it to break it in....

Ok got out and shot it. Not one single problem at all from any of the 5 mags I was trying yesterday. Everything was smooth as silk.

I did run into one other problem though. It shot left. Way left, as in I have no windage correction left. The sight is as far right as it will go. I'm thinking the front sight might be canted a touch, but to the naked eye it doesn't look like it.  I figure i can just tap the FSB to the left a little tiny bit and see what that does,.

it's funny though I have ARs that shoot to different sides the other one was shooting right, and the rear sight is almost all the way over to the left might just ahve to try and adjust that one too a bit.