When dealing with a collectible , be gentle! There is NO WAY putting a rifle stock in the dishwasher is going to help it, long term.. It will absorb water, and eventually shrink, usually more than original, and OFTEN CRACKING in the process. That stock has spent a long long time getting into equilibrium with it's environment, and now it will go thru a stress greater than when it was first cut and put in the kiln. Yes, I am quite sure it will get rid of the grime- So will paint stripper in a dip tank- both BAD ideas if you want any semblance of patina or originality. I would as soon stick one of my Chileans thru a wide belt sander as a dishwasher.
Over on parallax bills site there is a lot of info on cleaning old stocks.