20 mm caliber is a specific size of popular autocannon ammunition. It is 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 | ![]() |
20×42 mm | |
Denel NTW-20 | ![]() |
20×82 mm Mauser | |
Denel Vektor GA-1 | ![]() |
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Vidhwansak | ![]() |
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Anzio 20 mm rifle | ![]() |
20×102 mm | |
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 | |
Şahi 20-102 | ![]() |
[2] | |
Metallic RT-20 | ![]() |
20×110 mm Hispano | |
Yugoimport-SDPR M71/08 | ![]() |
Single barrel development of Zastava M55 | |
Oerlikon KAA/KAB | ![]() |
20×128 mm | Formerly known as Oerlikon 204GK/5TG |
Meroka CIWS | ![]() |
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Oerlikon KAD | ![]() |
20×139 mm | 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 20 mm F2 |
The usual nomenclature of ammunition indicates the diameter of projectile and the length of the cartridge that holds it; for example, 20×102 mm is a 20 mm projectile in a 102 mm long case.
Though this designation is often assumed to be unique, this is not always the case, e.g. there are three different 20×110 mm types which are not compatible. These may be distinguished in that some cartridge designations may include additional letters or names as a suffix, e.g. the various different types of 20×110 mm might be distinguished as 20×110 mm Hispano, 20×110 mm RB and 20×110 mm USN.