I use one of two things, when I need to strip a stock:
With appropriate precautions, neither is dangerous.
With appropriate application
, either will cut through the old finish in a heartbeat.
It's a bit of a moot point in this case, but acetone does have a drawback. It draws the natural oils and waxes out of the wood it comes in contact with, so it should only be used when an oil finish is going to be applied during the re
-finishing phase. In this case, though, you've got 90 gallons of cosmoline in that stock. So, you have two choices: 1. Draw all of the cosmoline out (and the natural oils, with it). 2. Refinish it without drawing out the cosmoline, and pray like mad that it doesn't bleed out in the future. Neither is fun.
As for your question...
No, the rest of the finish will not be easily removed with sandpaper. Mosins don't give it up that
Keep stripping it via some kind of chemical application. Once you have at least 95% of the vanish/lacquer/cosmoline removed from the surface, you should be able to go to abrasives and/or a steam iron.
My preferred finish is 70/30 Mineral Spirits/Tung Oil until the wood is sealed. Then I finish with a 90/10 mix of Fromby's Matte Tung Oil (it has additives) to standard Tung Oil.
Refinishing a milsurp stock is a lot of work. If you intend to hand-rub an oil finish, and wet-sand the stock... you'll be blown away at just how long it takes.
Don't wear yourself out before you even get to that point. Let the chemicals do the work.
I need a new signature. This one sucks.