Okay, got the XCR to the range for it's second session. Sent 210rds downrange without a hiccup, and was getting cocky. The gun was pretty hot, so I put it aside for a half hour while I shot other things. When I tried it again, no bang. Rounds were stripping from the mag just fine (I tried another mag just to make sure), but the gun wasn't locking up. No strikes at all. Extraction took some grunt, though. I got it to shoot a couple of times by feeding manually, but that only worked 50%. Just got it home and stripped. It's a little dirty, but nothing seems loose or broken. What could it be?