If you're looking to strip it right off and apply a new finish, it's really easy to make it look great.
Use paint thinner to strip the shellac, get it all out and don't be shy with the thinner. You can use 0000 steel wool and stiff tooth brush to scrub off the shellac, it's what I have used before and it works great. Don't scrub too hard.
You can then let it sit overnight to dry or wait a couple hours and do the whole thing over to make sure you got it all if you are doubting yourself as to wether you got it all out of the wood.
Usually one stripping will do just fine. After you are happy with the removale of the old finish let the stock dry for at least a day, I usually wait two to make sure she is dried right out.
For the sanding I use 150gr and
very lightly go over the whole stock. Do not oversand it, you don't want to remove any more wood than you have to. I'll usually go over the whole thing once more with 220 grit or thereabouts to give it a smooth finish.
Use a can of duster or a compressed air hose if you have them to get all the wood dust off the stock. You can just use a wetted soft cloth but then you'll have to let the stock dry again overnight before proceeding.
The finish I use is boiled linseed oil mixed with a dash of paint thinner. You can get boiled linseed oil (BLO) at any home depot. Just pour some BLO into a container that has a resealable lid, say maybe about 50 ml into it. Then pour a capful or so of paint thinner into it and give it a good shake with the lid sealed. The thinner will thin out the BLO so when you apply it, it will run deep into the pores of the wood carrying the oil with it, as it dries out the thinner evaporates and leaves the oil behind. That's the idea as it was explained to me by my brother who is a master woodworker. Works awesome for him and me so far lol good enough.
What you want to do is get some of the mix on your fingers, don't be shy, just dip your fingers right in and slather it on the stock. Start in one area, I usually break the stock down into sections, so I'll start with the buttstock. Just rub that stuff into it using your bare hands. Rub it in in circular motions at first using moderate pressure. Once a whole area is saturated start doing long hard strokes with the palm and build up some friction heat and really work it in
(thats what SHE said! 
).
Do the whole stock in this manner. You should use enough of the mix that by the time you are done there will still be some excess wet spots of oil on the surface of the stock. Use a clean cloth to lightly damp away the excess oil. Let the stock dry for at least 2 days in a nice warm spot in the house that isn't too damp or cold (ie not the garage or a humid basement).
The next coats you will do take your 0000 steel wool and lightly rub the stock down with it
going with the grain! This will open the pores back up for the next application you are about to do. After the steel wool use a cloth again to lightly clean anything that might be sitting on the stock. Repeat the oil mix application process.
I usually do this about 7-8 times.
The process is as simple as it gets and the results are amazing!
I basically figured this method out from talking to my brother and reading numerous websites on gun and furniture finishing lol
Here's a couple stocks I did myself using the above method exactly:
You get better and better at the finer details the more you do. I even started ironing out the dents in the stocks before the sanding step to really restore them back to original beauty.
This is the latest one I did which is by far my best. It's a 1944 Soviet Mosin M44. The finish was a flakey crusted shellac and there were a lot of dings and dents in her. Again I used the above method (also with some minor ironing/raising of the dents before sanding):
You can see for such a simple method it really does work very very well.
Let me know if you need any more details on how to do it, I'll be glad to help man!
Cheers!
