Presuming it's not a scope problem (probably not with 3 different scopes) or a barrel riding problem (free floated), I would guess if there is an issue, it's that the dovetails for the scope mounts weren't machined coaxial (in line with) with the reciever longitudnal axis (unlikely in my opinion), or that the front face of the receiver, where the barrel tightens, wasn't machined off square. Hard to check for these kind of conditions. Since it sounds like it shoots OK, maybe it's not a problem after all. YOu should be able to see a 12" misalignment by boresighting. Set your scope back to "neutral", and bore sight. See if there is really a 12" error.
HTH, Tom