I'm in the grind one you have to fit camp. As above, there are likely lots of variations in specific M500 stocks over the years. A quick search of Midway found a Hogue and Limbsaver sold as pre-fit to the 500 and 835, but you may run into the same issue. I'm assuming this is a bird gun. Check out a slip on leather recoil pad. They are much better for mounting a gun on flying game than any sort of rubber pad that will snag and stick to clothing. Remove any existing pad, cut or shim to proper length of pull with your pad attached (you can change the mount angle slightly here also if you desire) slightly round the edges of the back of your stock, apply a thin plastic spacer with screws and grind it "close" or hardface the wood with some poly and apply the slip on leather over the top. Slick as goose poop shouldering the gun on fast flushing or crossing birds. You'll find it a very nice upgrade for a cheap field gun if you adjust the LOP to fit you. If your game is target sports with mounted gun such as trap and skeet, or slugs for deer, the rubber "grabby" pads with a pronounced curve are a positive feature.