06-20-2013, 04:15 AM
It's an occasional problem in gas guns. It sounds like the projectile jackets are getting caught at a deformity in the gas port. I had this happen with an 18" select match Douglas barrel for an SPR. Bore scope analysis revealed a large chunk of metal protruding from the gas port, which had developed after about 200rds as well. The gun started out shooting 1/2" easy, then opened up noticeably, hence the bore scope analysis. Eventually, the metal bugger broke free and it returned to shooting well.