The difference between 44 special and 44 black powder bullets?

The .44 S&W Special is a cartridge currently loaded with smokeless powder, as opposed to earlier cartridges such as the .44 Colt or .44 Russian. Those cartridges, generally considered obsolete, were loaded with black powder. Smokeless powder should not be used in firearms built for black powder- the pressures are too high to do so safely. You may also find .44 caliber BULLETS (not cartridges) intended for use in a black powder revolver. These are typically made of a very soft type of lead, different from the harder lead alloys (lead-tin-antimony) used in modern firearms.