I have a rifle built up to the bushmaster varminter. Shooting Winchester 45gr bulk pest ammo from Wal-Mart, at 100 yards, it tags .22MOA. Only issue i have had with it is it is a picky eater, and you gotta clean it well. Every 100 rounds, I run some solvent through the bore. If you are feeding it good ammo, and its clean, then check the crown, as well as the scope mounts. Even a LITTLE play in those mounts can throw your groups wild. 'QD' mounts will add at minimum 1 MOA. Make sure you get properly setup for cleaning, autos are a little trickier than bolt actions. Get some chamber stars to get those damn lugs, as grit in there can also throw a curve at ya. If its clean, mounts are tight, and the ammos good, then it probably needs to go back to BM.
*EDIT* Splelling