Whiting and acetone works but is slow. Here's another that is much faster but more expensive. It is quite popular with the double shotgun hobbyists. The problem might be finding a tank big enough for a regular rifle stock.
Get a disposable aluminum roaster pan at the supermarket that is large enough for the
stock. Stop by your Home Depot or whatever and get a gallon of acetone and a
gallon of alcohol. If the stock has a plastic finish you might want a can of
some paste stripper too. Use that first if the outside finish requires it. If
the stock has a varnish or oil finish the acetone will lift that with no
problem. Then toss the stock in the roaster and pour in the acetone (it will
also neutralize the paste stripper). Cover the wood until it floats. Then pull
off a good length of aluminum foil and make a cover for the "tank", sealing it
as well as possible. Be aware that acetone is highly volatile and smoking the
cigar over the top of it is not recommended. Let the things soak for several
days, turning the wood over a couple times a day. When you feel like you're
tired of that, and the acetone looks like it has quit changing color, pour the
acetone back in the can, rinse the roaster out with alcohol, and then soak the
stock in the alcohol just like you did in the acetone. When you yank the baby
out of the alcohol bath it will be CLEAN! And you can seal it and refinish it
anyway you want after you let it dry a couple days
RWO