.22 CB Cap (Conical Ball Cap ) is a variety of .22 caliber rimfire ammunition which has a very small propellant charge (usually no gunpowder, just the primer), resulting in a low muzzle velocity of between 350 and 853 ft per second (107 and 260 m/s). This is similar to the muzzle velocity produced by a low to mid-power .22 pellet gun, however the bullet from a .22 CB cartridge is significantly heavier than a typical airgun pellet and therefore carries more energy.
Designed to be a cross between the .22 BB and .22 Short, and first catalogued in around 1888 (though probably first made before that), it "managed to combine about all the disadvantages...[of both] into one generally useless cartridge", being no more accurate than either while being noisier than the .22 BB Cap, and also penetrating much deeper requiring a backstop as strong as the .22 Short, and thereby negating the BB Cap's advantages for shooting indoors. However, the cartridge found use in Europe in cheap rifles meant for short range pest control well into the twentieth century.
American ammunition manufacturers dropped it in the 1940s, while RWS in Germany, Eley-Kynoch in Britain, and Alcan continued to offer it into the 1970s. In some European countries, 6mm Flobert cartridges are still manufactured and sold, as they are used in "Flobert revolvers" which are usually unaffected by gun laws (e.g. in Czech Republic and Slovakia, Flobert revolvers fall within the same weapon category as air rifles), and they are also used in antique firearms chambered for the .22 Short and the .22 Long, as most modern ammunition is of a much higher pressure than the old black powder cartridges these guns were chambered for.
Due to their low power, CB rounds can be trapped by most pellet gun traps. This will however result in significant bumps in the pellet trap, and is not recommended. In longer rifle barrels the CB has a very quiet, seemingly non-existent report due to the lack of residual pressure at the muzzle (see Internal ballistics). However, the CB loses velocity fast in longer barrels, due to the lack of anything other than the primer as a propellant.
The original .22 CB cartridge has the same case as the .22 BB, but there are now low-power .22 rounds sold as .22 CB Short and .22 CB Long which come in the more common .22 rimfire cartridge cases. The .22 CB primer fired rounds has a reduced powder load and is kept between 350 and 720 ft/s, while the regular .22 Short has an increased powder amount, and launches the same 29 gr bullet around and above 1000 ft/s. So while having the same length, the modern primer fired .22 CB Short & Long rounds, and the regular .22 Short are different cartridges. Other modern rounds, such as the .22 Aguila Colibri and .22 Aguila Super Colibri have bullets in the same weight range as the regular CB Cap with velocities in the 300 ft/s to 500 ft/s range, essentially making them somewhat weak CB Caps in .22 Long Rifle cases. The longer cases of the CB Short & Long and the Colibri rounds, will allow the rounds to be fired in magazine fed firearms, in which the tiny CB Cap cases would jam.