New guy needs some help.

[velo555]

My AAC barrel is pinned and has set screws (dimpled)

[robrob]

I assume the spent case is being ejected normally.

Will the bolt hold open on an empty mag? Fire it with one round in the mag. This tells you if the bolt is short stroking.

Try another lower that you know functions--borrow one if you have to. This will confirm it's the upper.

AAC is a great company. If you don't feel comfortable pulling the gas block send it back to them.

[speedjunkie]

It is a factory AAC PDW upper, so my builder had nothing to do with dimpling.

The spent case is ejected normally, and no, it won't lock the bolt back on an empty mag.

I borrowed a Spikes H2 buffer to try, will try my other lower as well, and swap BCG, just to rule it out. If all that fails, the GB is coming off.



Mike

[Wo0dzm3n]

It is a factory AAC PDW upper, so my builder had nothing to do with dimpling.

The spent case is ejected normally, and no, it won't lock the bolt back on an empty mag.

I borrowed a Spikes H2 buffer to try, will try my other lower as well, and swap BCG, just to rule it out. If all that fails, the GB is coming off.



Mike

Perfect plan.

[speedjunkie]

Well, I'm really not any better off than before. Tried the buffer, it sort of locked the bolt back, but wouldn't strip a fresh round. Swapped lowers, and it ran better, but locking the bolt back was still iffy. Swapped buffer springs, no joy. Tried swapping buffer tubes today, still no resolution. It will cycle a few, but won't lock the bolt. So, I'll take the GB off just to see. Need a heat gun tho, set screws are loctited on.




Mike

[speedjunkie]

Got to shoot it today after hosing and blowing out the gas tube. First round locked the bolt back solid. Subsequent rounds didn't fair as well. I could get 2-3 in a row, then fail to strip the fresh round. Even tried heavier reloads, no help. Called my class III dealer to see about getting it shipped back to AAC, removing GB, or letting him play with it for awhile. Guess I'll update later when I know more. Thanks all for the suggestions.



Mike

[speedjunkie]

Received a RMA from AAc this morning. Say 2-3 weeks, hope that holds. Will advise what they find.




Mike

[speedjunkie]

Thought I should post an update. I remembered I had a Young NM bcg in another upper. Weighed it, it's the same as a FA carrier. So, I swap bcg between uppers and notice something. The Young literally falls in place, while the AAC seems to be catching. The bolt locking lugs seem to be binding on the barrel locking lugs, and actually putting the bcg in a slight bind. To verify, I ran the Young in the AAC upper, ran like a top. Ran it in my 16" upper, ran like a top. Contacted AAC with my findings, they wanted the whole upper back. So, it went back to the mothership 2 weeks ago. Hopefully hear something back soon.



Mike

[Sky_DiveR]

Sounds like an out of spec bolt or carrier. Good job troubleshooting the problem. Not too much to these things once ya get to know how it works.

[speedjunkie]

Sounds like an out of spec bolt or carrier. Good job troubleshooting the problem. Not too much to these things once ya get to know how it works.

Definitely the carrier, as I swapped bolts between carriers with no change. Should have caught it sooner though. Wasted a lot of ammo finding it.




Mike