On a working gun I always use Tung Oil (100% pure). No finish lasts forever and Tung Oil can have coats added right over the old coats without stripping. Just a 30 second pass with 0000 steel wool and more Tung Oil can be applied. Dries thoroughly over night. I even use it on furniture!

I have lost count on how many times my M60-7 has been touched up! The great part is there is no sanding or stripping so no grip size reduction happens and it's very nice and easy to do. Tung Oil never peels!