It's like a Betty Crocker cook book on this thread, everyone has a pet recipe. My favorite way is thick black plastic and alot of sunshine, but this time of year I fall back on my Black and Decker heat gun (had to buy it after I burnt up the wife's hair dryer), but you have to go very slow and easy. I really like the idea of the furnace duct and the heater, I might try that one this winter. One way to get alot of it out of an SKS is probably the most fun. Wipe off all you can with an old rag, then buy a case of ammo and a batch of stripper clips. Take her out and shoot her until the barrel glows. You might want to wear a shirt you're not too attached to.
