I use a Weaver base for the Thomson Center Contender. I use medium rings if I can, high if I must. The scope base has a cantilever that I set up to reach to the back of the receiver ring. I try to set the scope up so that the flared eypiece isn't over the action opening or is towards the rear of the opening. Some variables with large adjusting rings get in the way. I lean to fixed power scopes especially on the Martini's.

The problems isn't the cartridge hitting the scope, it's getting your fingers in to load the gun.