Various combinations of subsonic rounds and semiautomatic .22 LR firearms result in unreliable cycling of the firearms' actions, as the result of insufficient recoil energy. Some subsonic rounds use heavier bullets (achieving lower velocities) to ensure, as a result of increased bullet mass, that enough energy is produced to cycle common blow-back actions. As an example, the Aguila .22 LR SSS "Sniper SubSonic" round, has a 60 gr (3.9 g) bullet on a .22 short case, providing the cartridge the same overall dimensions as a .22 long rifle round. However, other problems may be encountered: the heavier and longer bullet of the Aguila cartridge requires a faster barrel twist (by the Greenhill formula) to ensure the bullet remains stable in flight.
Two performance classes of .22 rimfire subsonic rounds exist. Some subsonic rounds, such as various .22 short and .22 long "CB" rounds, give about 700 ft/s (210 m/s) velocity with a 29 gr (1.9 g) bullet providing relatively low impact energy (41 J at muzzle). 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. The Aguila SSS gives about 950 ft/s (290 m/s) velocity with a 60-gr bullet offering energy (163 Joules) equivalent to many high velocity .22 long rifle rounds using standard 40-gr bullets. Other heavy-bullet subsonic rounds give similar performance, and are intended for hunting of small game, or control of dangerous animals, while avoiding excessive noise.
Many .22 LR cartridges use bullets lighter than the standard 40 gr (2.6 g), fired at even higher velocities. Hyper-velocity bullets usually weigh around 30 to 32 gr (1.9 to 2.1 g) and can have a muzzle velocity of 1,400 to 1,800 feet per second (430 to 550 m/s). This higher velocity is partially due to the use of lighter bullets.
Later hyper-velocity rounds were introduced by other makers, based on the long rifle case with lighter bullets in the 30-gr weight range and slow-burning rifle powder loadings. The overall length of many of these cartridges was less than the overall length of the standard 40-gr bullet long rifle cartridge. One example is the Remington Viper; another is the Federal Spitfire.
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 US Army Air Corps procured the Savage Model 24 .22 LR/.410 combination gun as an air crew survival weapon included in the E series of survival and sustenance kits, primarily to forage for game for food. The .22 LR full metal jacket bullet ammunition was issued with these firearms for military use to comply with treaty restrictions on expanding bullets.
The traditional .22 rimfire cartridges (BB, CB, short, long, extra long, and long rifle) differ in construction from more modern cartridges in the way the bullet is constructed and held in the case. Bullets for traditional .22 rimfires are the same outside diameter as the case but are constructed with a narrower cupped "heel" on the base of the bullet which is inserted into the case. 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. The bearing surface of .22 rimfire bullets is often lubricated and the surface is exposed to contamination. This was a common design in the early black powder cartridge era.
Because the .22 long rifle round commonly uses a heeled lead or lightly plated bullet, the nominal bullet diameter is larger than the nominal bore diameter to prevent excessive lead fouling that can occur when shooting lead bullets that are the same or slightly smaller than the groove diameter. SAAMI specifies a nominal bullet diameter of 0.2255 with a tolerance of -0.004, while the specified bore diameter is 0.222. In practice, 0.224 or slightly larger bullets are common, with barrel groove diameters commonly around 0.223. 2b1af7f3a8