Polyurethane will do a good job. I've been using Minwax Helmsman Spar Urethane for quite a while now, and am pleased with the results. If there are some dings on the stock, and I assume there are, the lighter ones can often be raised by using a damp cloth over the area and pressing a hot iron on it for a few seconds. The steam will often raise the dent. Repeat the process as needed.
The stock will tell you when it's done most of the time. Good luck, and take your time......