Rimfire

A rimfire is a type of firearm cartridge. It is called a rimfire because, instead of the firing pin striking the primer cap at the center of the base of the cartridge to ignite it (as in a centerfire cartridge), the pin strikes the base's rim. The rimfire cartridge is essentially an extended and widened percussion cap which contains not only the priming compound, but also the propellant powder and the projectile (bullet). Once the cartridge has been struck and discharged it cannot be reloaded, as the head is deformed by the firing pin impact. While many different cartridge priming methods have been tried, only rimfire and centerfire survive today in significant use.