The mix of potassium nitrate and powdered sugar used for rocket fuel is either rammed tightly into the rocket motor, or melted and poured into the motor, in both cases forming a solid "grain" of fuel. This then burns at a rate slower than our black powder, though a solid grain of black powder can also be used for a rocket motor. In fact, this is how the Estes brand of hobby model rocket motors are made; with black powder.
While the mix of KNO3 and powdered sugar itself might not burn as quickly as conventional black powder, the interesting question is: Does the addition of a small amount of powdered sugar make our BP better in any way??
It seems like such a simple and obvious query that we CAN'T be the first to propose it, but we still won't know 'till we try...
;~)
Vettepilot