I refinished my Browning that had a poly finish. I used a furniture stripper to soften and remove some of the finish but that stuff is tough. It took a lot of scrubbing with the stripper and a stiff nylon brush in the crevices and tight corners. But I found that once the finish is softened from the stripper, a single egde razor blade )or utility knife blade) drawn across the stock will remove the finish nicely. Just use the blade as if you were fleshing out a pelt. Hold it between the thumb and index finger of both hands and draw it toward you as you hold the stock between your knees. Be sure to keep the blade at 90* to the way you are pulling it so as not to cut into the stock.
Also, broken glass works good if you can find a piece with a straight edge.