Does it have to be actual black powder? You might want to experiment with Hogdon's Tripple 7. It is much cleaner than any black powder. I have used it in pistol cartridges... mostly .44 Special. Only drawback I found was that I needed to wash the brass in water for reloading... something you gotta do with any black powder cartridge... which are unmentionable on this forum, BTW.
Obviously, if you are gonna be shooting a Damascus barrel, you need to get it inspected, and you might want to use a reduced charge weight with the T7 loads if you go that way. As some Damascus guns have been shot with smokeless powders, I would guess T7 will work if the barrel is in good shape. You probably want to use their 2F granulation.
It has no sulfur in it, so no rotten egg smell and no corrosive residue.... but you still gotta clean the gun after shooting it... with hot soapy water. I use Murphy's Oil Soap... and remember to put some kind of oil in the bore when you are done. Use a well-oiled wool mop. Something that will penetrate any rough spots in the bore preferably as all Damascus guns I have seen in the past forty years or so have been pretty scary-lookling.
Another poster here with more experience shooting Damascus guns might give you some advice regarding barrel lube(s). I just don't shoot 'em. Never did. A Damascus gun that is intact has a certain value as a wall-hanger, blown up they are scrap metal.
Dunno your experience level loading BP shotshells, but be careful. BAD THINGS can happen at the loading bench.
If you try T7, please PM me with your results. I am curious.