I got some Burris rings that have plastic inserts that will compensate for this (mounting holes off center). It takes a lot of range time to get them just right. If I remember right they are called Burris Z rings.The culprit usually turns out to be that the base mounting holes in the receiver are off center. That sucks a lot, because as I understand it, it's iffy tryin' to fill the old holes and drill new ones because the temper of the receiver can be altered.