The .22 Long Rifle rimfire cartridge is a long established variety of ammunition, and in terms of units sold is still by far the most common in the world today. The cartridge is often referred to simply as a .22 LR and various rifles, pistols, revolvers, and even some smoothbore shotguns have been manufactured in this caliber. The cartridge originated from the Flobert BB Cap of 1845, and was developed by the J. Stevens Arms & Tool Company in 1887. For many decades, it has been a very popular cartridge around the world. It is one of the few cartridges that are accepted by a large variety of rifles, as well as pistols. Virtually every manufacturer of cartridge firearms makes at least one model chambering it, and this has been true for more than a century. The .22 Long Rifle and related cartridges use a heeled bullet, which means that the bullet is the same diameter as the case, and has a narrower "heel" portion that fits in the case.
The low cost, minimal recoil, and low noise make the .22 LR an ideal cartridge for recreational shooting and pest control, and it is often purchased in bulk. The standard box of .22 LR contains 50 rounds, and .22 LR is often sold by the brick, containing either 10 boxes or loose bullets for 500 rounds, or the case containing 10 bricks for 5,000 rounds. Some boxes also contain 100 rounds.
.22 LR ammunition is available in a very wide variety, and a very wide price range. Bullet weights range from 20 to 60 grains (1.9 to 3.9 g), velocities from 350–1,750 feet per second (110–530 meters per second). "Promotional" loads for plinking can be found for under US$20.00 per brick ($0.04 per cartridge), while precision target rounds can cost US$80.00 to upwards of US$250.00 per brick. Currently, a standard box of 50 rounds goes for US$1–3. For comparison, a box of 9x19 mm Parabellum, another popular and relatively inexpensive round for semi-automatic handguns, costs closer to US$8–35 per box of 50. It is common to shoot well over a hundred rounds on a single shooting range visit. For rifle shooting, the price difference is even more dramatic as powerful rifle cartridges like .308 Winchester and .30-06 Springfield can approach and exceed US$1 per cartridge. For this reason especially, .22 LR is commonly used by hunters for off-season target practice. They are also the ammunition used by Boy Scouts for the rifle shooting merit badge.
The low recoil and high speed of a .22 LR cartridge in pistols make it suitable for introductory firearms courses. Because errors in technique are not covered up by the increased recoil of a "defense-caliber" handgun, they can be more easily identified and corrected before moving to more powerful handgun cartridges like 9 mm, .38 Special/.357 Magnum, or 45 Auto (45 ACP). Additionally, some firearms chambered for common calibers such as 9mm Parabellum and .223 Remington (5.56mm) can be converted to fire .22LR with the use of special barrels and mechanism assemblies.
Annual production is estimated at 2–2.5 billion rounds.
22 LR is effective within 150 meters (490 ft), although practically this range will be much less. After 150 meters the ballistics of the round are such that the large "drop" will be difficult to compensate. The relatively short effective range, low report, and light recoil has made it a favorite for use as a target practice cartridge. The accuracy of the cartridge is good, but not exceptional; various cartridges are capable of the same or better accuracy. A contributing factor in rifles is the transition of even a high-velocity cartridge projectile from supersonic to subsonic within 100 yards (91 m). As the bullet slows, the shock wave caused by supersonic travel overtakes the bullet and can disrupt its flight path, causing minor but measurable inaccuracy.
The trajectory of the standard high-velocity .22 LR with a 40-grain (2.6 g) bullet has a 2.7-inch (69 mm) rise at 50 yards, and 10.8 inches (270 mm) low at 150 yards, when zeroed for 100 yards (69 mm rise at 46 meters, and 274 mm at 137 meters, when zeroed for 91 meters). A .22 LR rifle needs to be zeroed for 75 yards (69 m) to avoid over-shooting small animals like squirrels at intermediate distances. The newest commercial rimfire, the .17 Mach 2, is based on the .22 LR case, but is slightly stretched in length (case length is similar to the CCI Stinger) and necked down. The light, aerodynamic .17 caliber (4.5 mm) bullet gives a much higher velocity than the .22 LR, for similar energy and a much flatter trajectory, but at the expense of increased cost and noise.
As a hunting cartridge, the .22 LR is mainly used to kill small animals such as rats and squirrels. It is also highly effective on rabbits at distances closer than 150 yards (140 m) and on ground hogs, marmots, and foxes closer than 80 yards (70 m). It has been successfully used on large creatures such as coyotes, but range should be limited to no farther than 65 yards (59 m); head and chest shots are mandatory with the most powerful .22 cartridge the hunter can use accurately. Hunters should find which cartridges, out of the various high-velocity and hyper-velocity ones, shoot well for them by preliminary testing.
A .22 LR bullet is relatively underpowered when compared to larger cartridges, but dangerous nonetheless: it can easily kill or severely injure humans and large animals. Users should therefore take great care to ensure there is no possibility of a stray bullet flying beyond its intended target and hitting someone or something else. Even after flying 400 yards (370 m), a stray .22 bullet is still traveling at approximately 500 feet (150 m) per second, which can inflict a very serious wound, and a standard .22 cartridge can have a ballistic range of up to a mile and a half (2400 m). Ricochets are more common in .22 LR projectiles than for those fired using higher powered cartridges as the combination of unjacketed lead and moderate velocities allows the projectile to deflect, not penetrate, and not be destroyed when hitting hard objects at a glancing angle.