What you are looking at is very similar to what the block shooters are working on. Clean barrel and dirty barrel, and any other different barrel conditions will make a difference in different guns. Shooting turkey patterns is different than shooting patterns for most small game. Lines in barrel, forcing cone, no forcing cone, barrel diameter, choke length and diameter, dirty or clean barrel all can be factors, in the gun. Then you have all the variations in ammo. I once shot a block gun, that shot good, for a few shots with a fresh coat of spray paint sprayed down the barrel and left to dry. What I have seen is many times when you get one shooting real tight by using a tight choke, you can loose some consistency in point of impact, when shooting on paper, on game you would probably not even notice.