By shear off do mean "broke" the tip off? wouldn't that put small parts in the gun? FIrst I would check the ammo, then I would check for too tight a chamber (just drop your head space gauges in it), then I would make sure it had all the springs it was supposed to have. Then I would make sure it wasn't way over gassed. Then I would make darn sure that the bolt carrier and bolt kind of line up with the extention and aren't battering against each other. Traprs first rifle did this and we were somehow lucky enough to get it to work, but I don't remeber how.....Oh now I remeber, I actually had it in my hands to see what it was doing, and Trapr ain't no slouch when it comes to figuring guns out as well