My first suggestion is to put the gun in some sort of "Lead Sled" device to take some variables out of the equation.... such as human error, and TRIGGER PULL! You would be surprised at how much groups improve when the rifle does'nt move any tiny bit while the trigger is being squeezed. And, let the barrel cool completely between shots....this should take the "action and/or barrel to stock presure" out of the equation also. Then all your left with is crown (which I doubt is it, but still possible) and ammunition.