AA#2 should meet your requirements. It take a smaller charge then most powders, burns clean, meters well, and it's accurate and consistant.
For the price of cast bullets, you could buy FMJ 9mm for about $15-$20 more per thousand and forget all the mess and headache from lead and lube in the air/gun. That's not much money at today's prices.
Mostly it gets energy from the Nitro. Burn speed is controlled by various means, and high Nitro content powders come in various speeds.but it gets its quickness from a heavy dose of nitroglycerin
rsrocket1 do you have any pictures of power pistols light show? If not I'll have to buy some to compare with longshot. These two pictures are of a 12 guage benelli and a .357 1911 coonan with longshot.