This last time, I did use one....SO MUCH cosmoline....and my stock was likely an oil finish rather than shellac, as I didn't find a hint of it anywhere.....oddly, the buttstock was nearly totally dry...and the grain was raised and hairy....but the rest of the stock was absolutely oozing the stuff out.
I found that getting it just to the point of boiling the cosmo, that it helped bubble out the filth....but you have to wipe fast, it's like you need a third hand. You have to be careful not to scorch the wood though. If your stock has shellac, it might not be a good idea to get it that hot though...as it might just flake it off.