Have you ever had trouble removing the old finish on old gun stocks? Try spray on oven cleaner. I buy it at Dollar Tree for $1.00 a can. Make sure it's the kind that contains lye. Be sure to remove any metal from stock and be sure to wear rubber gloves and eye protection. After leaving it on for a few minutes it usually comes right off with the use of steel wool. Better than sanding as it doesn't remove any of the wood and sanding will just gum up your sandpaper. Wipe down till stock is dry, wait at least a day, then apply your new finish.