The .22 Long Rifle cartridge is a rimfire rifle cartridge that is the most popular cartridge for use in rifles as of 2015. The bullet of the .22 LR has between 141 and 259 joules of energy at the muzzle of a typical firearm depending on the specific loading used.
The .22 LR round had a number of historical ancestors, though the most direct were the .22 Long and .22 Extra Long. Firearms manufacturer J. Stevens Arms and Tool Company produced the .22 LR by combining the case of the former with the bullet of the latter. Though not a particularly powerful or accurate round as compared to other types of rifle ammunition, the .22 LR proved to be adequate for pest control and hunting small animals. Combined with its low recoil and low cost, the .22 LR quickly became popular as a round for training, practice and recreational shooting. Many variants of the .22 LR exist, including subsonic rounds and high-powered hypervelocity loads.
The .22 LR is almost unique among modern rifle rounds as it is a rimfire cartridge. Rimfire ammunition is ignited by a weapon's firing pin striking the rim of the cartridge. In contrast, most other popular cartridges such as the .30-06 and 5.56 NATO round are centerfire rounds.