Just to add to what Cayugad mentioned,Pyrodex is classified as a smokeless powder by DOT.
It isa littleharder to ignite than blackpowder - but is safer to handle and store. Pyrodex is not classified as an explosive like blackpowder is - thus the reason why blackpowder is harder to find.

If I'm going to use either one, I buy the finer granules because it ignites quicker in many MLs - plus it burns cleaner. Pyrodex P is the equivalent to FFF powder found with real blackpowder. Either one is what I use occasionally in all my MLs from 45-58 caliber.