do you reload? if so try seating the bullet closer to the rifling.
if you do not reload, start looking for problems with the rifle, since the ammo is going to be the same no matter what. is the barrel touching the stock, is the scope mount loose at all? did you loc-tite it?
How about the trigger? too stiff to be precise? have someone else shoot it and see if they have the same problems.
-Matt
