Ruger 10/22s have two problems. First, the front end of the receiver can be machined so that it will point your base (and therefore your scope) upward. This is called "the Ruger Hump". Second, the barrel clamp to the receiver only clamps at the bottom of the barrel, which acts to pull the barrel to point downward. Combine these issues with an older (1970s) Leupold 3x9 VXII with limited elevation adjustment, and you will not be able to sight in. The front of this mount is approximately .029" thinner than the rear of the mount, which effectively compensates for the Ruger Hump and barrel droop and points the scope downward to the point of impact. This allows you to sight in your scope with the elevation adjustment closer to the center of the scope's range of adjustment. I have done a lot of research to find this mount. It solves the problem.
Pros: Serves purpose
Cons: Not many
This review was written in the old system and had content requirements that are different than reviews written today.