> From what I've heard, when modern handguns were banned some shooters switched to modern reproductions of the mid-19th century models only to find that they didn't much like the cleaning (black powder makes a lot of mess), fiddling and slow loading that goes along with these guns.
One cleans black powder firearms with regular old soap and water, which is really interesting to me. I hear some people even just put them in the dishwasher!
A practiced shooter can load faster than you'd think, but using a powder horn and the plunger is still considerably slower than loading a cartridge revolver with a speed-loader or by hand. It is possible to make paper cartridges with pre-measured powder charges that can just be dropped in and then plunged. In that case it's almost as fast as loading brass cartridges one at a time, which is still considerably slower than modern alternatives. This is why American cowboys would carry at least two revolvers for a total of 10 rounds, or 12 if they were feeling brave. The reason why 10 is that there were no firing pin safeties, so if you got banged hard and there was a round in the top chamber it could accidentally discharge.
As an aside, in the USA a 19th century design muzzle loader isn't even legally a firearm under federal law. You can buy one on eBay and have it mailed straight to your door. I don't know if any of the states have restrictions, but so far as I know black powder firearms aren't really used for any kind of criminal activity except maybe poaching.