How tight was the screws torqued down on the ring bases? If it has deformed it, so it's out of spec, or bent, where another base wont tighten up on it, then you'll probably have to install a new rail. When tightening the scope base screws, use a torque driver, if you can get one, and tighten the screws 40-60 in/lbs. You can get a cheap 1/4" torque wrench from Harbor Freight, as it is not critical for an exact torque on these, just as long as it falls within that range. The torque varies between those numbers by the manufacturers.