I’m not sure how trade guns were normally done, especially for metal finish, but you might want to do some research on boiled linseed oil before going that route. At the top of the page you will find “search”, click on that and do a search on boiled linseed oil, you will get lots of reading on that subject. I’ve browned the only trade gun I did because I built it using walnut and thought browning would look better and less glare when hunting. Couldn’t have looked to bad, someone talked me out of it right after building it.