Buddy of mine built a 11.5” pistol and has run into problems when shooting his duty/home defense ammo through the gun. The failures seem quite severe and I don’t have a lot of experience with diagnosing AR15 failures so I was hoping someone has seen this before and may be familiar with it.
Quick summary:
He’s put 300 rounds of practice ammo through the gun without issue. The practice ammo is federal 55gr boat tail hollow point:
When he tried running some of his duty ammo through the gun it was choking badly failing to chamber almost every other round. This occurred when he was using gen 2 pmags and 20 round colt mags. When he switched to 30 round GI aluminum mags, it fed. Duty ammo is:
He didn’t take any pics of the malfunctions when it happened but kept a couple of the rounds that failed to chamber. They look like this:
The dents match up to the lugs on the bolt.
On the opposite side of the dents there is a deep gouge/scratch:
He described the orientation of the round in the upper when the failures occurred like this:
All parts used in build are new. He and I put it together. I’m built 7 rifles without issue. Used correct tools etc.
ADM Upper
Radian ambi lower
Geissele Super 42 buffer and spring in a milspec tube
LMT Enhanced complete BCG
Colt 11.5” FBI HRT barrel purchased from Shark Arms
When looking at his barrel extension in the upper I noticed that the transition from upper receiver feed ramps to the barrel extension ramps was not smooth like on all of the previous builds I’ve done. There is a definite ledge on each side and it appears worse on the left side.
Here’s what his upper/barrel extension looks like:
I have no idea if the barrel extension/upper fit is part of the problem, I just noticed it looked different that all of mine. Would love to hear some thoughts if anyone has seen this type of malfunction before. We have access to replacement parts to try and swap stuff out to see if something fixes it (standard bolts, BCG, carbine spring/buffer and a spare unused SOLGW upper).
Thanks for your time.
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