Hey:
I have a CVA mountain rifle of the same vintage. There's only a few moving parts in the line of ignition. Trigger,sear, tumbler, hammer, and the springs. Some screws too. The surface between the trigger and the sear arm should be smoothed slick. that will relieve some pressure. Hidden rust and too tight screws are the only things i can think of that will bind the lock. If you can take the lock apart, check for burrs on the bridle and lock plate in the area of the tumbler. The back surface of my bridle where it bears againt the tumbler was poorly machined and collected dirt and slowed things down. If not a good soaking of some solvent can drive rust and gunk out,(liquid wrench will loosen things up). :m2c:
Bill