Not going to try solve the rings/base issue but want to make two comments. Use either all steel or all aluminum mounts and rings. The two don't seem to work as well together for some reason.

Second, try a dab of 3M Scotchkote (sp?) it is almost like a rubber cement. Just a dab in the rings will solve a lot of slippage issues. I comes off with various solvent type products and leaves no ring marks unless over tightened.

“You never need fear a man, no matter what his size. When danger threatens, call on me, and I will equalize.”
Samuel Colt.

�Common sense is genius dressed up in work clothes.� - Ralph Waldo Emerson