I have had good luck with shellac and rottenstone. Steam out the dents as far as they will go, then use a rottenstone/shellac slurry to fill the remainder of the dents and the wood grain. Sand. Dye stain the wood to match the butt stock if needed. Then finish, preferably with ... shellac for at least one coat. The result is some dark spots that match the grain. You can also use shellac sticks as patch.