I'm not a ML expert, but a lot of the old flintlocks cannot use newer powders. You can always visit the websites and find the info, the best two blackpowder substitutes are 777 and Pyrodex, but they DO burn with higher pressures and aren't safe in all guns.
30point, did you have good success with Shockeys gold? It was the worst stuff I ever used, I fired rounds over a chronograph with it and got variations of almost 500fps! One shot would be around 1000fps, and the next would be under 600fps. Needless to say the groups were the size of an American car.