Asking for a friend, seriously. A buddy of mine just finished building an AR with sentinel arms barrel and spikes billet upper/lower combo. The rifle feeds reliably but wont shoot a pattern. Bullet strikes are all over the map. We thought we fixed it because the barrel nut had slightly loosened up. Torqued it back down and it shot great, then the problem started again. We retightened the barrel nut, but due to lack of light we were unable to test fire it again. My question is, what in the world could be making the barrel nut loosen up, and/or make this "premium" part rifle shoot like and AK that's been run over by a tank?