I think that gun has a lot of potential. The Murphys and steel wool is good advice though I think I would try some 2-0 wool to start. Go slowly and be patient. This sort project takes time and a lot of elbow grease something a owner can do and something many gunsmiths are not willing to do as it is not cost effective for them. After you get the gunk off you can start thinking about talking to a gunsmith. If there is pitting in the barrels that could sink the project. Doubles are all about barrels. Use light oil and steel wool on the outside of the barrels, get some blackboard white chalk and rub over the barrels after a rub with the oil and steel wool. This will pick up the rusty oil that could get in the pores of the metal and discolor the pretty Damascus
