Twenty millimeter caliber is a common firearm bore diameter, typically used to distinguish smaller-caliber weapons, commonly called "guns", from larger-caliber "cannons" (e.g. machine gun vs. autocannon). All 20 mm cartridges have an outside projectile (bullet) diameter and barrel bore diameter of 0.787 inches (20.0 mm). These projectiles are typically 75 to 127 mm (3–5 in) long, cartridge cases are typically 75 to 152 mm (3–6 in) long, and most are shells, with an explosive payload and detonating fuze.
Weapons using this caliber range from anti-materiel rifles and anti-tank rifles to aircraft autocannons and anti-aircraft guns.
Twenty-millimeter-caliber weapons are generally not used to target individual soldiers, but have targets such as vehicles, buildings, or aircraft.
Each weapon is listed with its cartridge type appended.
Weapon | Country of origin | Cartridge | Notes |
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Neopup PAW-20 | ![]() |
20×42mm | |
Denel NTW-20 | ![]() |
20×82mm Mauser | |
Denel Vektor GA-1 | ![]() |
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Vidhwansak | ![]() |
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Anzio 20 mm rifle | ![]() |
20×102mm | |
M61 Vulcan | ![]() |
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M197 electric cannon | ![]() |
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M39 cannon | ![]() |
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GIAT M621 | ![]() |
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ZVI PL-20 Plamen | ![]() |
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Nexter Narwhal 20A | ![]() |
Based on the M621 | |
Metallic RT-20 | ![]() |
20×110mm Hispano | |
Yugoimport-SDPR M71/08 | ![]() |
Single barrel development of Zastava M55 | |
Oerlikon KAA/KAB | ![]() |
20×128mm | Formerly known as Oerlikon 204GK/5TG |
Meroka CIWS | ![]() |
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Oerlikon KAD | ![]() |
20×139mm | Formerly known as Hispano-Suiza HS.820 |
GIAT M693/20 mm modèle F2 | ![]() |
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Rheinmetall Rh 202 | ![]() |
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Denel Land Systems GI-2 | ![]() |
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Nexter Narwhal 20B | ![]() |
Based on the 20mm F2 |
Cartridge type indicates the diameter of projectile and the length of the cartridge that holds it; for example 20×102mm is a 20 mm projectile in a 102 mm long case. Only rarely do two designers use the same case length, so this designation is usually definitive. Some cartridge types have additional letters or information about them listed. A B following the case length such as the 20X138B, indicates the cartridge has a belt which is used for headspacing. An R indicates a rimmed cartridge such as the 20X145R. An RB indicates a rebated rim, one which is a smaller diameter than the case head such as the Oerlikon 20X110RB.