For Hogpost:
The mass of ejecta, burned or unburned is equal. Mass of gas or mass of unburned BP is the same regardless of state. The only way to increase the mass of the ejecta is to add mass to the bullet or the powder. It can't magically happen at ignition.
I'm also challenging your statement that BP has a faster burn rate than SP. If it's true that BP ejecta is 50% unburned, by definition the burn rate is in fact slower than SP, as the burn "event" is of much shorter duration with SP. Not sure I could make the claim that 50% of the ejecta in an SP charged rifle is coming out of the barrel unburned. I suspect pressure/time curves would prove this out.
But that's just my opinion. YMMV.