While we hear a lot of hype of the "center fire speed -muzzle loaders" that's what most of it is.. hype. The average in line shooter will push 90-120 grains of powder. 100 grains being the average. That will give most projectiles around 1700 +-fps. While that's real good for the projectiles we use, a smaller projectile, while perhaps going faster just might not develop the energy need to cleanly dispatch large animals. When you do not have the speed necessary to get down range energy, the only alternative is to increase the weight of the projectile. Take for example the White rifle. Shoots 70 grains of powder and a 500 grain conical. The conical might be only moving at 1350 fps, but check the down range energy some time. Its amazing....

Small bores also fowl out faster.Since there is less diameter in the barrel, the burning of powder also fills the bore faster. Shoot a small .32 caliber squirrel rifle. You will understand.

I think the ballistics might have something to do with this question, but I really do not understand ballistics as much as I would like. I am sure some of these real shooters on the board might have a reason for the light weight black powder not working so well.