Many moons ago I did a how to on HSP stock recoil pad replacement and filling the hollow cavity with lead shot
So my here is the short version, put your HSP in the freezer over night, tell the wife to STFU NICELY, get a hammer and sharp putty knife ready, remove the stock and immediately use the putty knife/hammer to remove the stock Piece Of S... recoil pad, sand the stock with a sanding block to square it up, get a prefit or if this is a PSS stock a Medium Grind to Fit. LimbSaver, and install the recoil pad, grind to fit is easy as long as you have a belt sander, once the recoil pad is done shoot your weapon, if you need more reduction in recoil remove the recoil pad and mix up 5 minute epoxy and LEADShot(make sure to use lead and not steel) and fill the hollow cavity until full with the lead shot, let it dry and sand it so if needed so the recoil pad fits, the extra weight in the butt really helps to balance out the rifle, and 200-300 rounds prone won't hurt the next morning.