I had the same problem with my Matrix build. I had an Anderson barrel in it and damn near had to mortar the thing to eject a live round and it was still a problem after several 100 rounds. Barrel wouldn't shoot for schit either, 98 saw the crap groups it shot at the desert shoot a couple of years ago. Taking his advice, I bought a Faxon barrel and swapped it out. accuracy problem solved and live rounds ejected just fine. I took the Anderson barrel to a gunsmith friend of mine (didn't have anything to loose with it at that point) and he ran his chamber reamer through it. Said it was definitely undersized, mostly in the neck area. That's probably why the primers in the fired cases from that barrel where flattened more than from my other 308 AR (sign of high pressure). He said a loaded round would chamber much easier than before and the headspace was still good. I haven't put the barrel in anything yet to see if it groups any better but I don't have much hope on that front, I don't think a tight chamber would have much effect on groups.