Cosmoline is pretty easy to remove if you've got some undo-it-yourself skills. A metal trash can, old oven rack, a few 200w bulbs or a heat lamp, and lo! An Easy-Bake cosmoline oven. Works great to get all the slime out and it'll even bake the crap out of the wood. Tip: baking the stuff out in your kitchen oven is a great way to earn a divorce, a fire, or both.
Another route (if you and wiring don't get along) is to bag one of those hand-held steam cleaners. Don't buy one off an info-mercial; you'll prolly end up with another Wunder by Emerson. Try Lowe's or Home Depot. They don't clean kitchens or bathrooms worth spit, but they will heat up the cosmoline to the point it melts. Use a huge plastic storage bin ($12 at Wally World) to keep the gunk off your floors while you do it. This method is MESSY! Being heated steam it will swell the wood, so a light sanding is needed after the rifle cools.
Note: Cosmoline melts at temps above 120º and has a flashpoint of 360º. The oven (depending on the bulbs you use) will reach 140-175º range. The steam cleaner method will hit around 180º.
http://www.surplusrifle.com/shooting2006/lowheatmethod2/index.aspI'd follow the oven approach, with the changes listed in R. Ted Jeo's follow-up to the original article.
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Flakbait [Delta6]