On one of my doubles the top screw, under the top lever, slowly works counter clockwise when shooting. It doesn't become loose but starts in that direction. I mentioned to a gunsmith, unfortunately he is a couple hours away, and he said it can be fixed by adding a very thin piece of wood , kind of like a shim. As he explained it the screw needs the tension it would have when tightened to keep it in place properly. Does this sound right and is it just a matter of adding a very thin piece right under the screw?
