Probably a burr on the transfer port. Easy enough to clean up yourself. The O-ring Store is good for replacements.
Polyurethane is excellent for abrasion and tear resistance. However I strongly recommend smoothing the barrel lead-in with some 400 grit wet sanding. Possibly start with 320 if the machining marks are deep. Or if it’s misaligned, you may need to tweak the nose of the bolt or send it back if you’re not comfortable with doing that.
Really was my one big complaint about the Chief. Mine is in .22, but same complaint.An older one, and there have been some changes in the rifle from then, but it seems the bolt probe o-ring is still a possible problem.I had hoped they had addressed that issuel....evidently not.Actually, even those the issue o-ring is some odd, really thin, metric size...it's not the o-ring. It's the roughness of the o-ring seat that seems to chew them up.Getting the barrel off is simple. The barrel set screw on the front of the breech is loosened or removed, the barrel band cross screw is removed, and it pulls (or twists and pulls) stright off the front of the rifle.LIKELY that chewed the 3 o-rings on the barrel shank, as likely the breech the shank fits into is pretty rough. AT THE LEAT, you'll repace some of those 3 o-rings. At the most, you'll polish the worst of the roughness out of the inside of the reciecer (but do NOT want to actually enlarge the hole).I tend to be conservative, and use hand powered tools where ever I can for more control.I polished the lead in to the barrel and the "chamber" where the bolt probe o-ring seats with the barrel off and hand tools. Hand tools would basically be shaped wooden dowels (or BBQ skerers/chopsticks) with little pads of abrasive paper rubber cemented to them. Run them by hand, change pads when you need to, and only polish enough to kill the roughness.In a fit of "over kill", also deppened and amde wider the o-ring seat on the bolt to take a larger (nore common sized) O-ring. BUt that lead to a 3rd problem. It didn't fit the loading secion of the barrel. SO I had to polish the loading section a bit larger to let the slightly fatter o-ring slide though.Anyway...with the smoothness and the larger size race and larger sized o-ring (in .22) it worked out great...haven't had a bolt probe o-ring probem.
Thanks for the confirmation...thought they changed that (at least on the .22). Was my only breakage on the rifle (so far).Only other problem was the speed of the rifle being too fast out the box. Powerful, but too few shots (declining rapidly). YOur version with the adjuster likely would just need the adjuster backed out....my version, have to go in and play with spring tension more directly.