I think it all depends on when it was done.. linseed oil seems to be the usual for Mausers and SKSs... But then at times, some were just so slathered in the storage grease, that actually became the finish, which I guess technically, is still an oil finish. I have also read, some were just issued and handed to soldiers unfinished and the hand oils and other oils they used became the finish, I actually have one that's almost black in color.