20 mm caliber
Firearm caliber
From Wikipedia, the free encyclopedia
20 mm caliber is a specific size of popular autocannon ammunition. The dividing line between smaller-caliber weapons, commonly called "guns", from larger-caliber "cannons" (e.g. machine gun vs. autocannon), is conventionally taken to be the 20 mm round, the smallest caliber of autocannon. All 20 mm cartridges have an outside projectile (bullet) diameter and barrel bore diameter of approximately 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.
Usage
Types of ammunition
- High explosive (HE)
- High explosive incendiary (HEI)
- Armor-piercing (AP)
- Semi-armor-piercing high explosive incendiary (SAPHEI)
- Armour-piercing discarding sabot (APDS)
- High explosive fragmentation tracer (HEF-T)
- High explosive high capacity (HE-M)
- Penetrator with enhanced lateral effect (PELE)
- Target practice - inert projectile (i.e., PGU-27A/B)[1] Used for training (TP)
- Target practice tracer - inert projectile with tracer material in base for visual trajectory tracking (i.e., PGU-30A/B) (TP-T)
20 mm weapons
Each weapon is listed with its cartridge type appended.
Current weapons
| Weapon | Country of origin | Cartridge | Notes |
|---|---|---|---|
| Neopup PAW-20 |  South Africa |
20×42mm | |
| Denel NTW-20 | South Africa |
20×82mm Mauser | |
| Denel Vektor GA-1 | South Africa |
||
| Vidhwansak |  India |
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| Anzio 20mm rifle |  United States |
20×102mm | |
| Arash anti-materiel rifle |  Iran |
||
| M61 Vulcan | United States |
||
| M197 electric cannon | United States |
||
| M39 cannon | United States |
||
| GIAT M621 |  France |
||
| ZVI PL-20 Plamen |  Czech Republic |
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| Nexter Narwhal 20A | France |
Based on the M621 | |
| Şahi 20-102 |  Turkey |
[2] | |
| XM301 | United States |
||
| Denel NTW-20 | South Africa |
20×110mm Hispano | |
| Metallic RT-20 |  Croatia |
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| Truvelo CMS 20x110mm | South Africa |
||
| Yugoimport-SDPR M71/08 |  Serbia |
Single barrel development of Zastava M55 | |
| Oerlikon KAE (KAA/KAB) |  Switzerland |
20×128mm | Formerly known as Oerlikon 204GK/5TG |
| Meroka CIWS |  Spain |
||
| Oerlikon KAD | Switzerland |
20×139mm | Formerly known as Hispano-Suiza HS.820 |
| GIAT M693/20 mm modèle F2 | France |
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| Rheinmetall Rh 202 |  Germany |
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| Denel Land Systems GI-2 | South Africa |
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| Nexter Narwhal 20B | France |
Based on the 20 mm F2 |
Historical weapons
Cartridges
(incomplete list)
| Dimensions | Name | Date | Bullet diameter | Case length | Rim | Base | Shoulder | Neck | Cartridge length |
|---|---|---|---|---|---|---|---|---|---|
| 20.3х95R Ghan | 21 (.827) | 95 (3.74) | - | - | - | - | - | ||
| 20х150R | ~21 (~.827) | 150 (5.9) | - | - | - | - | - |
Naming conventions
The usual nomenclature of ammunition 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.
Though this designation is often assumed to be unique, this is not always the case, e.g. there are three different 20×110mm 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 20×110mm might be distinguished as 20×110mm Hispano, 20×110mmRB and 20×110mm USN.
Common suffixes
- B e.g. 20×138B: the cartridge has a belt which is used for headspacing, i.e. it helps ensure the correct positioning within the gun's chamber.
- R e.g. 20×145R: a rimmed cartridge: the diameter of the rim forming the base is larger than that of the cartridge case itself.
- RB e.g. Oerlikon 20×110RB: rebated rim, one where the rim is a smaller diameter than the case head allowing the extractor to follow it into the chamber, facilitating advanced-primer ignition, a recoil-moderating system.