My theory is that the finer the granulation of black powder, the more violent the initial explosion. this creates a pressure spike that has several negative effects in a smoothbore, primarily shooting shot, but also creates some problems when shooting a ball. A sharp violent explosion will try to force whatever is between the charge, and the obstruction ( be it shot column or ball) though the obstruction. If it shot, it most likely will blow a hole in the pattern, with a ball it will seek an escape route around the obstruction, either creating spin, or bonding the patch to the ball long enough to change the flight of the ball.
All the superfluous junk that we carefully stack into our “special” load is nothing but a buffer designed to deaden the effect of the sharp explosion generated by the wrong powder granulation. JMO!
Hungry Horse