Interesting, I need help with a gun....no make or model, might as well be, I need help with the air. Obviously the front and rear action rings are not level under that streight edge, so they are not the same height, if square. A scope base or bases should be level and centered to the axis of the bore as mounted.
First thing you need are bases or a base for that make and model action. Forget shims or Fouxinh up a scope mount job wih epoxy.
And if the base, or bases that are for that action don't fit correctly, then what.........?
Then you modify the bases: Get them as close as humanly possible, then glass bed them to the receiver. Rough up the bottom of the bases, and use release agent on the receiver. That way the epoxy is on the bases, and the bases are fit for that rifle/receiver. After that, you shouldn't even need to lap the rings. Pretty simple, and no I would not use soda pop cans or any other kind of shim.
