Gunpowder (propellant) drives in the bullet from the firearm as it burns. Types of powder include rolled ball, flake, lamel, and tubular. Primer usually consists of compounds of lead, barium, or antimony and is used to light the powder. It burns quickly when struck by a sharp blow of the firing pin. In center-fire ammunition, the primer is contained in a small metal cap that fits in the center bottom of the cartridge case. In rimfire ammunition, the primer is located in the rim of the cartridge case.