This might help:
At the range the other day a good friend was trying to get his new Savage zero'ed at 100 yds to start working on some loads. But couldnt get it even close. Ran out of "up" in the scope. Not a cheap scope. And I believe he was using weaver rings but Im sure this "problem" could/would pertain to most any make. When the rings were removed it was found that the recoil "key" in the ring's sat at a different height when the key was flipped over (thus allowing/forcing that ring to sit higher). And as it turned out he had installed the rear ring with the key upside down (or at lease opposite from the front) and with the 20 MOA base he had installed already put about 50 MOA of cant into the scope. More than it could recover from for a 100 yd zero. Let alone the fact that the different height rings tourqued his scope pretty good. Flip over the key, reinstalled, and zero was established easily.
Good luck.