20 M 621 20-mm helicopter cannon and THL 20 turret system (France), Guns - Integral and mounted

Development
The 20 mm calibre 20 M 621 single-barrel revolver cannon was developed at the request of the French Army by Manufacture d'Armes de Tulle (MAT), a division of the GIAT Group (now Nexter Systems). The requirement was for a lightweight, multipurpose weapon for use on both helicopters and surface vehicles. Initially designated AME 582, the gun programme began in 1957 and the first prototypes were delivered to the army for firing trials in 1960. As part of the army project, at least three helicopter mountings were developed to allow the AME 582 to be carried by several types of helicopter. The gun was intended for the following role: suppression of ground troops, armed reconnaissance, air-to-ground attack (including light armoured vehicles) and air-to-air self-defence. Three helicopter gun mounts were initially developed: the 19A floor mounting designed for the Eurocopter Puma/Super Puma/Cougar, and later adopted for Eurocopter Panther and Super Frelon; the 22A side fuselage mount for the Gazelle; and the 23A mount for the Ecureuil/Fennec. The 19A system has now been replaced by Nexter's lightweight SH20 system.In 1962, a requirement was issued by the French Air Force for an airborne version of the AME 582 for its helicopters that would use electrically primed M55-type ammunition and M12-type links. A pre-series batch of 70 weapons, which were re-designated AME 621, was produced between 1966 and 1969. Full production started in 1973 after several modifications to the feed system and the introduction of a nitrogen-treated barrel instead of the chromium-plated one. It

Description
The Nexter 20 M 621 is a single-barrelled, 20 mm cannon, which can be adapted for either left- or right-hand flat feed. It uses 20 mm M50 type (HE, AP, HI) electrically primed ammunition that is interchangeable with the US M56 rounds used for the M61A1 Vulcan. The cannon is 2.2 m long, 203 mm wide and weighs 49 kg. Its rate of fire is selectable between 300 and 740 rds/min or single round. The average recoil force is 400 kg, but with a muzzle brake in place of a flash eliminator, and using a shock-absorbing mount, recoil is reduced to 250 kg. The 20 M 621 has a muzzle velocity of 1,030 m/s when using HE/HI and 1,000 m/s when using AP. The barrel has a life of 8,000 rounds and the cannon life is 16,000 rounds. The gun fires international standard 20 × 102 ammunition. The HE explosive ammunition round, with optional tracer, weighs 100 g. It contains a charge of hexal and its auto-destruction fuze has built-in delayed arming and storage safety devices. The round explodes into about 40 splinters, which will penetrate 40 mm of hard wood at a distance of 1.5 m from the initial point of explosion. The AP hard core armour-piercing tracer round weighs 110 g, and is designed to be used against light armoured vehicles at ranges up to 800 m, being capable of piercing 25 mm of armoured plate. The HI incendiary round, which is fitted with a simple percussion

The complete article appears in the following publication:
Publication Title	Jane's Air-Launched Weapons
Publication date	Aug 10, 2011
Section	Guns - Integral and mounted
Publication synopsis	The only accessible and constantly updated guide to the world's inventories of airborne weapons. Covering well over 600 systems, in service or in development, it provides a detailed and comprehensive reference to: capabilities/technology; functionality/effectiveness; user base; combat record; upgrades, variants and future enhancements. The guide includes extensive analysis tables covering all weapon types, national inventories and aircraft weapon loads and documents the world's air-to-air and air-to-surface missiles, bombs, rockets, guns and underwater weapons, including new and emerging weapons.
Key contents include	Detailed review of worldwide events in the air-launched world. New systems, weapons tests/trials, combat details, contracts and deliveries, industrial moves and more Air-to-air missiles within and beyond visual range Air-to-surface missiles & direct attack, anti-ship, stand off and cruise missiles Bombs & precision and guided munitions, cluster and dispenser munitions, nuclear weapons, conventional unguided bombs Guns - integrated and mounted, podded systems Air-launched rockets Underwater weapons - mines/depth charges, torpedoes Analysis tables Contractors listings
Different sections provide in-depth detail covering	Air-Launched Rockets Air-To-Air Missiles - Beyond Visual Range Air-To-Air Missiles - Within Visual Range Air-To-Surface Missiles - Anti-Ship Air-To-Surface Missiles - Direct Attack Air-To-Surface Missiles - Stand-Off And Cruise Analysis Analysis - Air-To-Air Missiles Analysis - Air-To-Surface Missiles Analysis - Automatic Grenade Launchers Analysis - Bombs Analysis - Country Inventories - In Development Analysis - Country Inventories - In Service Analysis - Gun Pods And Mountings Analysis - Guns Analysis - In-Service Combat Aircraft And Their Air-Launched Weapons Capabilities Analysis - Mines And Depth Charges Analysis - Rocket Launchers Analysis - Rockets Analysis - Torpedoes Analysis - Worldwide In-Service Combat Aircraft Bombs - Cluster And Dispenser Munitions Bombs - Precision And Guided Munitions Bombs - Unguided Contractors Glossary Guns - Integral And Mounted Guns - Podded Systems Underwater Weapons - Mines And Depth Charges Underwater Weapons - Torpedoes Underwater Weapons - Unclassified Projects

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