I don't know. BP just won't build the pressure smokeless will, no matter how much you put in there even with a 50" barrel. I know they use bullseye in toy rockets as a subsittute sometimes for BP. Yes pressure plays a role. The BP never builds up enough pressure/heat to burn all the grains. The initial velocity pushes it out faster than it burns. I mean theres pressure vs heat curves for every burnable substance.