I’ve been shooting it. TLDR is in the last two paragraphs.
Before I installed it, I noticed that the top of the barrel was more textured than the bottom. And after I degreased the threads with brake cleaner it sat for a day. The next day, there were some specks of rust forming. At first, I thought nothing of these things, however….
It fed poorly during test firing with two different weight, known good, bolts. This was with Blue 147gr RN, which is somewhat pointy. Not a huge deal, since some lowers and some barrels are going to require tuning because blowback ARs aren’t standardized. Mine’s a PSA Colt mag lower that I SBR’d prior to realizing that PSA bubbafucked the ramps. Even though I fixed it and its reliably fed 5 digit rounds since, I can’t rule that out, so I’ll not blame the barrel. Anyway, I decided to do some polishing with Cratex and wet-dry. There were concentric circular machining marks on the feed cone, right where the noses were hanging up, so I polished those out without removing much material, and lightly broke the angular edges. I noticed at this point that the nitride is very thin and weak. In fact, it came off like bluing. Shitty nitride could explain the fairly rapid forming rust on the threads. When I looked at the outside of the barrel again, I noticed that the texture on the top doesn’t look like typical bead-blast, and wondered if it may be related somehow.
It feeds great now. I shot several mags, both full and partial, today with no stoppages using two different weight bolts. Both slow-fire, and hammer triples. Suppressed and unsuppressed.
None of this is necessarily a dealbreaker for me, since this is a budget barrel at a budget price, but if the feed cone starts rusting and causing stoppages where I polished it, I’ll scrap it and buy another XCaliber.