Just a guess here... but you seem to have everything but the kitchen sink clamped onto the 15-22 with the Surefire. Do you have so much on the other 15-22? Rifle weight can make a BIG difference. In any event, you might try swapping muzzle devices on each rifle at the range while leaving everything else alone and compare. My guess is that the muzzle device has little impact. But if it does...