A modern bullet is the front part of a "round" or cartridge. A cartridge consists of a "bullet", propellant and a primer. These are packaged in a metallic, paper, or plastic case which is sized exactly for the chamber of the firearm being used. When the rear of the case (containing the primer) is struck, an explosion in the back of the cartridge ignites the propellant. The controlled explosion forces the bullet out of the barrel. Cartridges have different ways of being loaded into different kinds of weapons. Cartridges can be loaded directly into a firearm into the chamber. Or, more commonly, into a clip, a magazine or other bullet container which is loaded into the firearm. Handguns known as revolvers have a cylinder with holes that the bullets are loaded into. Modern guns called pistols are handguns loaded with a magazine.