Bullets pushed into the lands will raise pressures and affect accuracy. If you are loading a hot load you could be raising the pressures way into the danger zone! First thing to do is reseat yor bullets to the proper length. Some guns will shoot better with the bullet close to the lands(subject is called "bullet jump"),but you must watch for signs of excessive pressure.
Also, you had the gun apart, not to sound silly, but make sure your scope and mountings are straight and tight. I had the guts of a scope come loose one time and the bullets kept drifting . Had to replace that scope.
Anyway, that's where I would start. Good luck, hope it helps.
