It hasn't been shot that much, its a pre-ban upper (the lower not the problem) and I've been told by a friend of a friend that tried to get it working for me that he changed out every part he could with his working AR, it still wouldn't work. It's also of unknown manufacture. The last option we can come up with is the gas port in the barrel is to small. Some links to specs would be nice, and if any AR gurus can come up with some ideas as to the possible problem would be appreciated. I would prefer to fix this upper than to sell it and buy a new one. Fire away with any question's, I'll try to answer as soon and as well as I can.