Quote Originally Posted by fusilier View Post
My understanding is that it has to do with efficiency -- that smokeless powders are more efficient, for some reason, with smaller caliber ammo. Not to do with fouling. I could be wrong though. The Lee-Metford (the immediate predecessor of the Lee-Enfield), was originally intended to be used with smokeless powder, but the British were having developmental problems with cordite and so it was designed for a .303 black powder round. Then it turned out that the barrel was ill suited for smokeless powders. :-/

EDIT --

Blackpowder weapons may have used looser fittings to allow for fouling to build up -- but I'm not sure about that.
Quote Originally Posted by Blackhawk748 View Post
Smokeless Powder has more bang than Black Powder so you need less for a similar punch, so they work better for intermediate cartridges because you get get a whole lot of bang for smaller space.
It isn't just a matter of "more bang". You can't throw a bullet faster than the speed of the propellant itself. The fastest black powder cartridges I can find (there's some examples of loose powder guns with very fine powder that go higher) were in the 1500 FPS range - decent, but not on par with smokeless. For example, the smokeless .30-06 Springfield can easily hit the 2900 FPS range, depending on loading. This is because smokeless has higher speed, and burns faster - allowing you to use a shorter barrel for a given charge.

This maximum speed doesn't translate into maximum power, because you can still add mass and use more powder to get the same speed. This is why black powder guns tended to be very large bore - to get that extra energy. Small bore guns have a lot of ballistic advantages, and smokeless can push a bullet faster - allowing you to get the extra energy with speed instead of mass.