Watch what Hugh is saying. He means cutting or sanding the outside of the grips and not the underside ridge. With original grips this should not be necessary after 50 plus years of usage. Make sure that you are installing them properly first, before you do any cutting. But maybe you have something very unusual. If your grips are still loose even after you fit them in properly, then try putting "O" rings on the screws. Don't crank the screws into place. but do tighten.
The proper size for the "O Rings" is:
#5 OR 3/8 x 1/4 x 1/16
These work perfectly on 1940 "42" and "Black Widow Grips".
17 cents at Home Depot.
Big Norm <img src="graemlins/wave.gif" border="0" alt="[byebye]" />