if it has a varnish type finish, this is what I would. put on some easy strip, or other varnish remover. it all works good. then I may lightly, lightly! sand it. do not get it out of shape, especially on the sharp edges and corners, it is easy to do. do not try to sand out the deep gouges, let the hot water do all it can with that, I don't try to make wood look brand new, because it will look like you did and I try to match it with the old worn bluing finish of the gun, that is all it needs,,,,,,,BLO and sanding is the plan for now.
Here is a new-be question.
I should take the finish off before trying to do anything about the oil stains?