I agree with cayugad on all of his comments. Here are few things I can add.

I find Blackpowder to be the most consistent igniting powder available. It produces tight velocity distributions, especially with 385 grain conicals and larger which simply seem to be unachievable, in my experience, with any other substitute, including pyrodex (though I haven't tried 777). Blackpowder, IMHO, is more flexible when tailoring loads for a particular purpose and seems, for me anyway, to be a powderwhere I can accuratately predict load performancebefore I actual shoot the load. No matter what quantity of BP I use, the results have been consistent.

Pyrodex is a good powder also. I have found it to produce more muzzle energy than BP witha notable exception. The exception is with 385 + conicals. The yield is just less than Black Powder, according to my chrony. But with 300 grain projectiles, pyrodex, especially pyro P, produce dramatically increased muzzle energies than black powder. The velocity distributions are wider, but since the velocities are high, they don't rear their ugly head at the target to any great degree until the range is beyond 100 yards. I think the greater the charge (to a point) of pyrodex the better the performance. It is not as forgiving at lower velocities as BP is. What I like best about pyro P is that it propels RB and ballet type conicals much faster than BP with very soft and thin fouling which can be , in the case of ballets,loaded over continuously.