So I finally decided to put an optic on my Savage Mark II, I had bought the scope bases some time ago and read they were Weaver bases. I purchased a set of Millett rings and Burris Zee rings, made for Weaver bases but sadly they did not fit; the cross sectional thickness of the bases seems too great for the Burris Zees to even slide onto and the Milletts could not be tightened down evenly and produced a cant. However, the rings fit perfectly on my Ruger 10/22 scope base, which is a combination of Weaver and 3/8 dovetail. Here's the Millett ring on the scope base: Yet it seems fine on the Ruger mount: Here I try to show the cross section, Savage on the left, Ruger on the right: Any advice would be greatly appreciated.
Get original weaver rings for those weaver bases, it has to do with the way the wedge on your rings grips the base itsself. Go to weaver optics.com and pick out a set of detachables. I've been mounting scopes for many years and this problem still comes up sometimes. I try to stay with a single maker for both rings /bases when I can. Weavers are still a great mount system I use them and Leupolds, with a cpl nato quick lever detach mounts for special scopes/rifles
Try flipping the clamping blocks on either side of the ring base 180 degrees. A lot of times they have different angles cut on each side to accommodate slightly different bases.