I would try damp #0000 steel wool first, lightly sand the wood, very lightly, and when smooth, I would try to match the stain as best that I can ! Keeping the steel wool damp, will stop it from taking too much Wood out. and go slow and lightly, don't let the wool catch and pull the wood up ! That's realy bad ! .Bill . It looks like the original owne used a brick,or paving brick to rest the rifle on, or some other hard rough object.