I am thinking your gas block is not to spec. This is the first I have seen or heard of this problem. Like Robo said earlier, since it is a new upper, take it back where you bought it and have them fix it. You shouldn't have this problem, no matter what ammo you run through it.
"Democracy is two wolves and one sheep voting on what to have for dinner.
Liberty is the well-armed lamb contesting the vote." - Benjamin Franklin
Last edited by fsted2a; 11-20-2012 at 09:19 PM.