I recently cut down a synthetic stock on a mossberg, I just made sure I kept enough of the area where you screw in the recoil pad to hold the pad in place. If you have to cut off too much to keep the screw holes in the stock, you can always cut and sand a block of wood (maybe 2inches thick?) to just fit into the stock and epoxy it in place. Then you can screw the pad into place using the wood to hold it. Then sand down the pad to fit the new stock dimensions.