.22 Long is a variety of .22 caliber (5.56 mm) rimfireammunition. The .22 Long is the second oldest of the surviving rimfire cartridges, dating back to 1871, when it was loaded with a 29 grain (1.9 g) bullet and 5 grains (0.32 g) of black powder, 25% more than the .22 Short it was based on. It was designed for use in revolvers, but was soon chambered in rifles as well. The .22 Long Rifle, a heavier loading of the .22 Long case, appeared in 1887, along with the first smokeless powder loadings of the .22 rimfires.
The .22 Long has the same case length as the vastly more popular .22 Long Rifle, but differs in that the Long Rifle has a significantly heavier bullet, a longer overall length (due to the longer bullet used), and a higher muzzle energy. The .22 Long is essentially obsolete; no new firearms are designed specifically to use it, and the largest 3 producers of .22 Long ammunition ceased production (although it continues to be made by CCI, Aguila, and others). Many .22 Long Rifle guns will chamber and fire the shorter round, though the .22 Long generally does not generate sufficient energy to operate semi-automatic guns. The one prominent survivor of the .22 Long is the .22 CB Long, a long-cased version of the .22 CB.
While the original .22 Long loading used the same powder charge as the .22 Long Rifle, and the .22 Long bullet was significantly lighter, the combination does not result in higher velocities for the .22 Long when fired from a rifle. The large barrel volume to chamber volume of a .22 rimfire rifle means that the powder gasses have expanded as far as they can in well before the muzzle of a normal length rifle barrel, and the light .22 Long bullet doesn't have the inertia of the .22 Long Rifle. This means that the .22 Long bullet (and to a lesser extent the .22 Long Rifle, in most loadings) actually slows down significantly before it exits the barrel.
Since the .22 Long Rifle performs as well in a short handgun barrel as the .22 Long does, and outperforms it significantly in a long rifle barrel, the development of the .22 Long Rifle assured the .22 Long's path to obsolescence. In a sense, though, descendants of the .22 Long still live on, though they are not sold as such.
Hypervelocity loadings of the .22 Long Rifle use bullets as light as 30 grains (1.9 g), and special blends of powder to make full use of a rifle barrel to generate velocities far higher than normal loads, and chamber pressures high enough to cycle semi-automatic firearms reliably. The most well known of these is the CCI Stinger, which actually goes so far as to stretch the case length slightly, so that with the short, light bullet, the overall length is still within the max overall length for the .22 Long Rifle.