The .22 long rifle, also known as the .22 LR or 5.7×15mmR,[4][5] is a long-established variety of .22 caliber rimfire ammunition originating from the United States.

Ammunition produced in .22 long rifle is effective at short ranges, has little recoil, and is inexpensive to purchase.

Its minimal recoil and relatively low noise make it an ideal cartridge for recreational shooting, small-game hunting, and pest control.

Beginners shooting firearms beyond their comfort level frequently develop a habit of flinching in an attempt to counter anticipated recoil.

Many handgun manufacturers have an upper pistol conversion kit to make it shoot .22 LR ammunition.

These conversions allow shooters to practice inexpensively while retaining the handling characteristics of their chosen firearms (with reduced recoil and muzzle blast).

Additionally, .22 LR cartridge conversion kits allow practice at indoor ranges which prohibit high-power firearms.

This can usually be mitigated by swapping the conversion kit for the standard bolt carrier group and firing several full-powered rounds to clear the gas port and tube of any accumulated lead fouling.

[11] Promotional loads for plinking can be purchased in bulk for significantly less cost than precision target rounds.

The relatively short effective range, low report, and light recoil have made it a favorite for use as a target-practice cartridge.

A contributing factor in rifles is the transition of even a high-velocity cartridge projectile from supersonic to subsonic within 100 yd (91 m).

[15] A .22 LR rifle needs to be zeroed for 75 yards (69 m) to avoid overshooting small animals like squirrels at intermediate distances.

These may not use any, or only small amounts of gunpowder, and have the characteristics of rounds intended only for indoor training or target practice rather than hunting.

Where these are in .22 LR form, it is only to aid feeding in firearms designed for the cartridge, rather than older .22 CB shooting gallery rifles.

Other heavy-bullet subsonic rounds perform similarly and are intended for hunting small game or controlling dangerous animals while avoiding excessive noise.

These rounds generally do not develop these velocities in handguns because their short barrels do not take full advantage of the slower burning powder.

Smokeless powder loads, called "high speed" or "high velocity", were offered by the major ammunition makers, giving a typical velocity increase of 8% (1,200 feet per second (370 m/s) to 1,300 feet per second (400 m/s)) while still using the standard 40 gr (2.6 g) solid or 36 gr (2.3 g) hollow-point lead bullet.

The CCI Stinger was the first hyper-velocity .22 LR cartridge and provided a significant increase in velocity and energy over standard rimfire rounds.

Such rounds have either a longer brass case that is crimped closed or a translucent plastic "bullet" that contains the shot and shatters upon firing.

During World War II, a full metal jacket bullet version of the .22 LR was developed as the T-42 for the suppressed High Standard HDM pistol.

The 1961 Army and Air Force technical manual for small-arms ammunition lists the jacketed cartridge as the M24.

The case mouth is then crimped around the heel, leaving exposed the majority of the bullet bearing surface that contacts the barrel of the gun.

Today, rimfire rounds are mainly used for hunting small pests, for sports shooting, for plinking, and for inexpensive training.

[30] As a defensive cartridge, it is considered inadequate by many, though the small size allows very lightweight, easily concealable handguns which can be carried in circumstances where anything larger would be impractical.

Despite their limitations, people can use .22 LR pistols and rifles for defense, and they are common simply because they are prevalent, inexpensive, and widely available.

The low volume of powder gases means that .22 LR suppressors are often no larger than a bull barrel; the Ruger 10/22 and Ruger MK II are common choices, because of their reliability and low cost, and the resulting product is often nearly indistinguishable from a bull barrel model (although weighing far less).

[32][33][34][35] The Israeli military used a suppressed .22 LR rifle in the 1990s for riot control and to "eliminate disturbing dogs prior to operations", though it is now used less often as it has been shown to be more lethal than previously suspected.

[31] Some other examples include the use of suppressed High Standard HDM pistols by the American OSS, which was the predecessor organization of the CIA.

(Commission Internationale Permanente pour l'Epreuve des Armes à Feu Portatives) rulings the .22 long rifle can handle up to 170.00 MPa (24,656 psi) Pmax piezo pressure.

Note: actual velocities are dependent on many factors, such as barrel length of a given firearm and manufacturer of a given batch of ammunition, and will vary widely in practice.