22 mm grenade
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The 22mm rifle grenade is inserted over the firing mechanism on the front of rifles that are equipped with the appropriate spigot-type launcher, either in the form of an integral flash suppressor or a detachable adapter. As with most rifle grenades, it is propelled by a blank cartridge inserted into the chamber of the rifle. A 22mm grenade can range from powerful anti-tank rounds to simple finned tubes with a fragmentation hand grenade attached to the end. The "22mm" refers to the diameter of the base tube which fits over the spigot of the launcher, not the diameter of the warhead section, which is much wider. This differs from conventional launched grenades, such as the US 40mm grenade, which are measured at their widest point, since they are launched out of gun-like barrels. Thus, a 22mm rifle grenade can easily be as powerful as a 40mm grenade, in spite of the seemingly smaller size. A 22mm grenade is launched on the spigot principle, like a spigot mortar; a tube slightly under 22mm is attached to the end of a rifle barrel to serve as the spigot, and left open on the muzzle end so bullets can be fired through it. The grenade consists of a heavy warhead section of 30-50mm in diameter for the nose, and a lightweight hollow tube for the tail section. The inner diameter of this tube is 22mm, and fits over the tube attachment on the muzzle with only a small amount of play, to create a good gas seal and promote accuracy. There are typically a series of rings machined around the perimeter of the tube, which serve as baffles to slow any escaping high-pressure gases created on launch until the grenade is clear of the launcher, and sometimes a metal o-ring to create a final seal and to lock the grenade in place until pressure has risen high enough.
To fire the grenade, first, a special blank cartridge is loaded into the weapon. There is often some sort of cutoff device on gas operated rifles that can be engaged to disable the gas piston, both to eliminate the possibility of a live round chambering itself, and to prevent any of the gas being tapped off, which might affect the accuracy and range of the grenade). The tail of the grenade is slipped over the muzzle attachment, where it indexes itself so the aiming mark is on the top. The rifle is lined up with the target, butt to the ground (as shown in the photograph above), and held to the proper angle to ensure the correct ballistic trajectory, a skill which must be learned in training. This can be done by eye, as in the photograph, but some rifles, such as the Yugoslavian M59/66 SKS variant, have built in flip-up ladder sights that allow for accurate ranging of the shots, by giving a graduated series of "rungs" which correspond with various ranges. The rifle is aligned with the target, and the user looks through the ladder sight, adjusting the angle until the sighting mark on the tip of the grenade matches the proper range on the sight. Then the trigger is pulled, and the high-velocity gases rush down the barrel, when they are slowed by the obstructing grenade fitted over the end, the low-pressure, high-velocity gas transforms into low-velocity, high-pressure gas very rapidly, forcing the grenade off the launcher at a relatively high rate of speed, whereupon it follows a ballistic arc to the target. A rifle grenade cannot be easily or safely fired directly at a target, and must always be fired in a ballistic arc; the closer the target, the higher the angle the rifle must be held, much like a mortar.
The first rifles to utilize the 22mm grenade were the American M1903 Springfield, M1 Garand and M1 Carbine, all of which required an adapter (the M1, M7, and M8 grenade launchers, respectively). After the formation of NATO, the 22mm grenade was adopted as its standard rifle grenade. Many NATO small arms, such as the West German Heckler & Koch G3, French MAS-36/51, MAS-49/56 and FAMAS, British SA80, and American M16/M4 are equipped to launch 22mm grenades without an adapter. Some non-NATO firearms, such as the Yugoslavian SKS, M70 and Spanish CETME (which predated Spain's entry into NATO) are also compatible with 22mm rifle grenades, and Israel employed a 22mm adapter for the Mauser K98k rifle.