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An automatic grenade launcher or grenade machine gun is a grenade launcher firing rounds in quick succession from an ammunition belt or large-capacity magazine.
These weapons are often mounted on vehicles or helicopters, as when these weapons are moved by infantry the weapon, its tripod, and ammunition, are a heavy load, requiring a small team of men. The Mark 19 Automatic Grenade Launcher, first fielded by the Americans in 1966, and still widely used today, weighs 62.5 kg, when attached to its tripod, and loaded with a box of ammunition. The popular Mark 19 is capable of indirect fire to 2200 metres, an indirect fire role traditionally reserved for mortars. Even though it carries less explosive than a 60mm mortar, this is thought to be counterbalanced by its higher volume of fire.
The most popular caliber for automatic grenade launchers in the west has been 40mm. The Soviet Union successfully fielded a 30mm grenade launcher, the AGS-17 during its war in Afghanistan, and in 2002, Russia introduced a successor weapon, the AGS-30. Traditional munitions for automatic grenade launchers include high explosive, fragmentation, shaped charge for attacking light armored vehicles. Less lethal rounds, like tear gas and sponge rounds, for crowd control, have also been made. In the 21st Century integrated sighting systems started to be sold, capable of detonating air-burst grenades precisely on, above, or behind targets the user designated to the sighting system.
Different weapons use different methods of operation, with the "blowback" and "long recoil" being two popular choices. In all these weapons the energy released by firing the previous round powers loading the next round into the weapon's breech. The popular Mark 19 is automatically reloaded through the blowback method, where expanding gases blow back the firing bolt.
In the long recoil method the bolt is fixed to the firing chamber, and the whole firing chamber is blown back. These weapons are slightly less accurate, but weigh less than blowback weapons. General Dynamics manufactures a long recoil weapon, the Mark 47 Automatic Grenade Launcher, as does the Spanish firm Santa Bárbara. The LAG-40 manufactured by Santa Bárbara has a relatively low rate of fire -- 215 rounds per minute.