That's not an uncommon occurrence when changing ammo. I think you're seeing the difference in the resonance of your barrel. I assume you mean a Remington Model 7 which has a shorter barrel than the Model 700, for example. I believe you'll see this occur with shorter, lighter barrels more often. If you had setup the rifle for the CT moly's first, you would be wondering why the Sierra's are shooting to the left. If you want to see this in spades zero a Ruger Mini-XX and then change ammo.