Brownells sells hard rubber spacers and I have used various woods for the same task. I even once bought a Weatherby Varmitmaster that had the prettiest piece of figured rosewood used as a spacer!! The spacers from Brownells can be had in various angles and tapers to allow a bit of adjustment in the pitch of the butt. You will know they are there but don't look especially bad. Bye the way I did remove the spacer from the Varmitmaster but only because it made the rifle nearly unusable for my pull...
