Since this last posting, my gunsmith/machinist has advised me of a quick and very easy way to remove the old finish completely if you want to refinish the wood. He recommended a spray product by SuperTech, called Brake Parts Cleaner. It will work on the old oil or varnish finishes, but does not work good on any of the epoxy or polyurethane hard finishes. Just spray on and immediately wipe off with "0000" steel wool. After that, wipe down with a clean rag and follow your normal procedure for wood refinishing. It only takes two or three sprays to remove all the old finish. CAUTION: HIGHLY FLAMMABLE AND VERY HARMFUL VAPORS. USE OUTDOORS ONLY. It is much easier to use than a varnish remover.
UPDATE: 4-9-20 This product has been taken off the market for some reason. I have tried several sources and they all say unavailable. I bought another brand of Brake Parts Cleaner, and it WILL NOT remove the finish on 3 different stocks I tried it on.l