Here's a thought. Put the winchester ammo back in the cabinet and go buy you some hornady 55 or 50 grain v-max ammo and try again. I think your just getting some inconstancy out of the ammo your shooting, or shooter error, possibly hammering the trigger a little too much. That is of course, everything is nice and tight on the rifle. Don't get too carried away with cleaning, and try not to string too many shots together with the 250, they warm up rather quickly and could affect your groups as well. Good luck.