I bought an Armalite 9mm AR from PSA a couple weeks back. Thing was a damn jam-a-matic. Fail to feed every 1-2 shots using Glock magazines. Sent it back to them and scheduled to get it back Monday. We shall see. The times it didn’t jam it was way FUN.
Could be buffer size, but PSA lowers are supposedly notorious for the ejectors not being adjusted correctly. Mine was jamming every other round until I bent it correctly. With the magazine out, you can look and make sure there’s a gap between the ejector and the bolt carrier. If it’s not an equal space, then bend the ejector around with a pair of needle nose pliers and you should be in business. I adjusted mine and have put more than a thousand rounds through it without any failures to feed or eject.