The .221 Remington Fireball, often simply referred to as .221 Fireball, is a centerfire cartridge created by Remington Arms Company in 1963 as a special round for use in their experimental single-shot bolt-action pistol, the XP-100. A shortened version of the .222 Remington, it is popular as a varmint and small predator round while also finding use among target shooters.