Dunno what RAR stocks are made of, but betting that sandpaper will get the better of it quickly. Plus, it's self-regulating. The paper side of a sheet of sandpaper shouldn't damage a rifle barrel, but if it does, it's an RAR. Just rattle-can it. If marking the barrel is really a concern, just remove the barreled action and substitute a wooden dowel of correct size and sand away.
