Rimfire ammunition refers to a type of metallic firearm cartridges. It is called rimfire because the firing pin of a gun strikes and crushes the base’s rim to ignite the primer. Invented in 1845, by Louis-Nicolas Flobert, the first rimfire metallic cartridge was the .22 BB Cap (AKA: 6mm Flobert) cartridge, which consisted of a percussion cap with a bullet attached to the top. While many other different cartridge priming methods have been tried since the 19th century, only rimfire technology and centerfire technology survive today. The rimfire .22 Long Rifle cartridge, introduced in 1887, is by far the most common ammunition in the world today in terms of units sold.