Without ammunition, a firearm is no more than an inefficient club. For this reason, much of the technological development effort in firearms history was devoted to ammunition. Essentially, ammunition consists of four parts: powder, projectile, primer and cartridge case.
Blackpowder Loads For muzzleloading firearms, a cartridge consisted of a measured quantity of powder and a lubricated projectile held in a paper, wood or vellum tube. In use, the shooter typically tore open the paper or removed the cap on the wooden tube and poured the powder down the barrel. He then removed the bullet from the cartridge and pushed it down the barrel on to the powder using a ramrod. The gun was then primed with a small quantity of powder or a percussion cap and fired. Wooden tubes were reusable; paper and vellum cartridge tubes were discarded. Later, paper tubes were treated to enhance combustibility so the whole cartridge could simply be rammed down the barrel without first separating the components.
Modern Cartridges A modern cartridge is defined as a complete round of loaded ammunition consisting of primer, propellant powder, bullet and cartridge case. Note that the bullet is only one part of a cartridge! Colloquial references to the "number of bullets in a gun" are technically incorrect. The correct term is the number of cartridges held in the magazine.
Normally, a cartridge for a shotgun is called a shotshell. A modern shotshell consists of five parts: primer, propellant powder, wad column, charge of shot pellets and shell case. In addition, caseless ammunition has been developed utilizing a solid propellant charge in place of the case, but this has not caught on with shooters.