For beginners, if you don't have wind flags out when shooting groups, your wasting your time. Yes subtle wind shifts or even mirage changes could easily produce the problem you are seeing. The load not being in tune would also cause this. Many times when a rifle "two group" the load is too hot.

All I can say is don't worry about the tang, or the crown, or screw torque as none of these things would cause this type of problem. Do not wait between shots as time moves on conditions change, and even if they look similar they are not. Do not worry about the bullet being in the lands, find the place where the barrel preforms the best. Just because a scope is new or a name brand don't automatically mean that it is working correctly. Pay attention to parallax.

Pay close attention to trigger pull, and watch that the cross hairs don't move when the trigger is slowly squeezed. This would also cause this problem. Pay close attention to the bench, or what ever your shooting off of, if it moves the POA will move with it. Last try some dry firing, a flinch as a reaction to recoil would also cause this problem. Before you get too concerned about this problem see if it repeats, and have another shooter try the rifle.

http://bulletin.accurateshooter.com/...-error-issues/