You can't fly with a can or horn of blackpowder, correct?
You CAN fly with ammunition in checked luggage,. I would pour my BP into cartridge cases, plug the ends with wax, and take them as "ammunition". I'm reading that the maximum "ammunition" that can be carried (per passenger) is 11#.
edit: spent shotshell cases would work too, either use a nitro card over the powder, or fold crimp the cases shut, but I would still use an over shot card if fold crimping. A "box" of 12ga should hold enough.
https://www.tsa.gov/travel/transporting-firearms-and-ammunition