You have to have a consistent bed for the rifle to shoot off of from one shot to the next shot. We bed our rifle actions so the action sits in the stock the same from shot to shot. A rifle moves a lot between when the trigger breaks and the primer is hit and ignited, you can see this movement when you set up your gun in your shooting rest and dry fire it, watch the crosshairs jiggle when the firing pin slams down and causes this vibration. This is all without recoil and torque of the bullet starting to spin when it hits the lands all of which cause more movement of the gun until the bullet leaves the barrel and final recoil. This is something that can't be prevented, can only be accommodated by allowing for this movement to be consistent. If a sling stud, pistol grip ect., is contacting on one shot and not the next it is unlikely the gun will move the same from shot to shot before the bullet leaves the barrel. Add to this a heavy cheek weld, no cheek weld, a death grip on the forend then a light grip, pulled hard into your shoulder and next a light hold or free recoil on one shot and not the next, a different position on the rest, trigger squeeze, consistency and many other things all will cause inconsistent movement of the gun before the bullet leaves the barrel. In other words you cannot prevent the gun from moving before the bullet leaves the barrel so one must focus on arranging for the movement of the gun before the bullet leaves the barrel is consistent from shot to shot if you want to shoot good groups.
