Seems like Black powder is a pretty powerful powder in of it self. I mean in the 1861 to 1865 civil war they hurled 9 lb steel balls with black powder. So if carefully select, and weighed, smokeless might work very well in muzzle loaders. Only problem is; no one quantifies the energy in a grain of powder of each type, but seems like everyone points to burn rate as the most important thing. Probably another factor is the bulk density of a given powder.