Bruce of mAss Backwards has a great post on how to remove cosmoline from a new rifle; a problem we’ve all had to face at one time or another. I think we all remember Easy Bake Ovens. Same principle, applied to guns.
UPDATE: I didn’t try Bruce’s easy bake oven for rifles, but the oven did the trick for me. There are advantages to living alone :) I have the Mosin-Nagant nearly ready to shoot, and will have to do a range report in a few days.