For those of you who puchase and shoot firearms that have been coated in Cosmoline, you know how much work it can be to get it off. Solvents work, but heat is better. Attached are pictures of the 'Poindexter Cosmoline Cooker'; a recent engineering marvel.
All you need are two pieces of 6" heater duct (buy the cheap ones), a 6" to 4" heater duct converter, and a heat source (see below). Depending upon your heat source, you might not need the converter.
There are two good heat sources: 1) A 4" removable food hydrator motor/heater unit. These work the best because they are made to run for a long time, or 2) A good hair dryer. I used a Nesco American Harvest food hydrator top until I dropped it an broke it; then I switched to the hair dryer.
All you have to do is put the two pipes together and put the firearm parts in the top (or bottom if they are small parts). Then put the top on and put the heat source in the top. I put the whole thing in a motorcycle oil drain pan with some oil dry (aka kitty litter). I could have used a small rag.
I added a meat thermomter to verify the temperature (drill a 1/8" hole near the joint to get an average temperature). Cosmoline melts at 135 degrees. The food processor motor put out 145 and the hair dryer was 145-155 depending upon how high the fan was set. When I was doing the barrel I used the 155, for the stock I used 145.
It takes a long time to heat an old steel barrel, mine is a Mosin Nagant 91/30 that I'm sure I could use as a crowbar. If you get in a hurry like I did then you will spend more time cleaning the bore. In 20 minutes the outside was clean and Cosmoline free. The stock I did in 20 minute intervals until it was clean - about an hour. The barrel takes at least an hour and the stock 2-3 hours if you aren't worried about ruining your wife's hair dryer. I'd suggest the dehydrator motor/heater and let it cook.
Pictures are below - cooker, thermometer, and top with the hair dryer stuck in it.