I usually scrape the old finishes off now including any space-age type epoxy types.
It's actually quite a fast process. Very clean as compared to using stipper soln's, which I've also done a lot of in the past.
A very sharp knife blade held at right angle to the wood is all that's needed. I use a common pocket knife quite often,,nothing fancy.
Use both hands on the blade,,your extra hand holds the tip of the blade and gives you control.
You can scrape on the forward or the backward cut. Use the thumb of the hand holding the knife to back up the blade and control the contact with the surface.
Nice clean curls of old finish are removed with each sweep accross the wood. Cross grain,,with the grain,,it doesn't matter. Choke up on the knife & blade to get into tight spots and concave areas. Light strokes are the best.
Old brittle finishes like shellac will sometimes break up upon removal but most just curl like planed wood. But you don't remove any wood unless you want to.
Leave the butt stock attched to the rec'vr. Leave the bbl attached to the frame and lock the bbl securely in a vise. That'll leave both hands free to control the knife.
After you get comfortable with the process,,you can sit down with just the stock in your lap to scape it down.
A 'cabinet scaper' wood working tool does the same thing. It's just that most people don't have one lying around & they can be a mystery to sharpen for some.
I go right to 220 or 280 grit garnet paper after scraping the wood. Then 320. That's good for most any factory style refinish on a production gun.
It shouldn't take all that long to prepare a butt stock & forend if there are no repairs or oil soaking to take care of.
Yes it's fun to bring one back to life. I still enjoy it and find myself spending time on some that are not really worth it in the long run. But I just can't seem to let them go.