So much advice . . .
Most furniture finishes will not be satisfactory on a firearm because of moisture from sweat, grease and oil from skin, and solvents and oils used on the firearm itself to clean and protect the firearm. These will lift waxes, fog polyester finishes, blister and soften paint, and penetrate the finishes and soften and destroy the wood. Use a finish that has been proven on firearms and is solvent and moisture resistant. There are many, but you need to make sure the one you choose is up to the task (read the recommended applications). TruOil, Permalyn, LinSpeed, Acra Coat for Wood, shellac, lacquer, solvent-based polyurethanes, and epoxies all will work well.
I do stock work for a living, and I prefer TruOil or Permalyn, but you can use just about anything you want. I have even seen stocks satisfactorily refinished with wood siding sealer, varnish, clear spray paint, paste wax, you name it. Just make sure you follow the right steps and you will get good results.
Sand the stock to 300-400 grit (always use a sanding block!!), wash the stock with a good degreasing soap (make sure you rinse it well), dry for several days, sand lightly, wipe it down with a dry cloth, seal the wood (first coat should be thin to seal the grain), let it dry for several days, sand the finish (give the following coats a smooth surface to stick to), build up several coats of whatever finish you choose to use (don't try for one coat coverage!!), and do a good job and you will likely be happy with the results.