Try cutting shims from a coke can (with plain old scissors) to match the contour/shape of the front & rear lower rings, and reseat the scope to see if it clears the barrel. You can "fine tune" this kind of spacing using several shims until the scope clears, since new/larger rings will otherwise raise the scope eyepeice higher than you might want relative to your cheek weld on the stock.
This is not as hokey as it sounds since soft drink cans are exactly 0.005" thick, cleanly cut, remarkably consistant, do not compress, take the shape of the scope/ring easily, cannot be seen, and are a permanent fixture once installed.