A few months back, you guys were trying to help me figure out what was wrong with my most current build (604). I thank you all for all of the effort. We left off with me having swapped bolt/carrier assy.. I also swapped lower (including buffer/spring/tube) I even swapped upper receiver. I did all of this swapping 6 times, (robbing parts from my other AR,s) I tried 5 different types of ammo. I had the sight base of numerous times cking to be sure gas was flowing properly through the sight base. I ckd the gas port size. I even installed a new gas tube (as a last resort). At this point it seems OBVIOUS, there must be something wrong with the barrel?????? So, I tried polishing the chamber (thinking the brass may be hanging up for too long during ignition. Well, I explained all of this to AR15Sport (where I got the barrel) and they were good enough to send me another barrel with a return shipping voucher. Yes, they trusted that I would return my barrel to them, after receiving my new barrel. What great guys to deal with! Anyhow, I installed the new barrel, and,,,,Yeah!!! It finally works. Heres a few pics.