[darkgael]

It is not just a matter of finding the right smaller amount of smokeless propellant.
The two systems are quite different.
Smokeless powders are ignited in and burn in a sealed system...first the cartridge itself and then, once pressure has sealed the cartridge to the chamber, in the barrel.

BP is burned in open systems - so to speak; you have a vent hole of some sort, whether it be the flash hole on a flint gun or the nipple under a cap.
Using smokeless powder in a system that can flash back is not a good idea.
Plus, the characteristics of smokeless powders are much influenced by chamber pressure - something which would be compromised in the open systems of MLers.
Pete