Do you know anything about wood-working, specifically finishing and such? Alot of guys say to use boiled linseed oil(B.L.O.) because its "authentic" but the rub on polyurethane apparently works pretty well for the gun stocks. I use the rub on poly. all the time just because its easy to put on and its looks good.
There is also polyurethane pre mixed with stain. Don't get this because it looks horrible.
But to strip the wood use something like 120 grit, to 180, to 200 sandpaper in that order(the smaller the # the coarser the grit) and maybe something finer than 200 if you want to. When your done sanding it, wipe it down with a rag soaked in mineral spirits to remove any sawdust.
If you decide to use the rub on, use a cloth. Make sure its not to spongy though. Wipe it on in a thin coat. It should be dry pretty soon, but it may be around 12 hours(haven't done this in a while). Take some 280 grit sandpaper and very lightly sand the poly. down until smooth and put more coats on. If you want grainy wood, don't use too many coats, but if you want like a plastic barrier on your stock 5+ coats is good.