20 mm caliber

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
A 20×102 mm round (second from left) with .50 BMG rounds, golf ball, and a stick of 168-pin SDRAM computer memory

Twenty millimeter caliber weapons are generally not used to target individual soldiers, but rather objects such as vehicles, buildings, or aircraft.

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 20×42 mm
Denel NTW-20  South Africa 20×82 mm Mauser
Denel Vektor GA-1  South Africa
Vidhwansak  India
Anzio 20mm rifle  United States 20×102 mm
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
Nexter Narwhal 20A  France Based on the M621
Şahi 20-102  Turkey
XM301  United States [2]
Denel NTW-20  South Africa 20×110 mm Hispano
Metallic RT-20  Croatia
Truvelo CMS 20x110mm  South Africa
Yugoimport-SDPR M71/08  Serbia Single barrel development of Zastava M55
Oerlikon KAE (KAA/KAB)   Switzerland 20×128 mm Formerly known as Oerlikon 204GK/5TG
Meroka CIWS  Spain
Oerlikon KAD   Switzerland 20×139 mm Formerly known as Hispano-Suiza HS.820
GIAT M693/20 mm modèle F2  France
Rheinmetall Rh 202  Germany
Denel Land Systems GI-2  South Africa
Nexter Narwhal 20B  France Based on the 20 mm F2

Historical weapons
Weapon Country of origin Cartridge Notes
Becker Type M2 20 mm cannon  German Empire 20×70 mm RB
Oerlikon FF  Switzerland 20×72 mm RB
Type 99 cannon, model 1  Japan
Ikaria-Werke Berlin MG FF/M cannon  Nazi Germany 20×80 mm RB
Mauser MG 151/20  Nazi Germany 20×82 mm
Ho-5 cannon  Japanese Empire 20×94 mm
Berezin B-20  Soviet Union 20×99 mm R[3]
ShVAK  Soviet Union
Helenius RK-20 APH  Finland Derivative of the Helenius RK-97 12.7 mm anti-materiel rifle
Ghan-Krnka fortress rifle  Russian Empire 20.3×95 mm R Bullet diameter 21 mm
Type 99 cannon, model 2  Japanese Empire 20×101 mm RB
Solothurn S-18/100  Switzerland 20×105 mm B
Bofors m/45  Sweden 20×110 mm
Bofors m/49  Sweden
Hispano-Suiza HS.404 and derivatives  Switzerland
Oerlikon F, FFL  Switzerland 20×110 mm RB
Polsten  Poland 20×110 mm RB
Colt Mk 12 cannon  United States 20×110 mm USN Advanced derivative of the HS.404
Madsen 20 mm anti-aircraft cannon  Denmark 20×120 mm
Type 97 automatic cannon  Japanese Empire 20×124 mm
Mauser MG 213  Nazi Germany 20×135 mm
Solothurn S-18/1000 anti-tank rifle   Switzerland 20×138 mm B
Solothurn S-18/1100 anti-tank rifle   Switzerland
ST-5 20 mm AA gun   Switzerland
FlaK 30 and FlaK 38 single-barrel AA  Nazi Germany Forerunner of Hispano-Suiza HS.820's post-war 20×139 mm round
Flakvierling quadruple-barrel AA  Nazi Germany
MG C/30L aircraft gun  Nazi Germany
Rheinmetall KwK 30 and KwK 38  Nazi Germany
Cannone-Mitragliera da 20/65 modello 35 (Breda)  Kingdom of Italy
Cannone-Mitragliera da 20/77 (Scotti)  Kingdom of Italy
Lahti L-39 anti-tank rifle  Finland Solothurn Long
Lahti L-40 anti-aircraft gun  Finland
Nkm wz.38 FK anti-tank vehicle-mounted gun  Poland Designated "heaviest machine gun", or "Najcięższy karabin maszynowy, Nkm", AA/AT (actually an autocannon)
Type 98 20 mm AA machine cannon and Type 4 20 mm twin AA machine cannon  Japan 20×142 mm
Bofors m/40  Sweden 20×145 mm R
Pansarvärnsgevär m/42  Sweden 20×180 mm R Recoilless rifle

Naming conventions

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.

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.

See also

References
  1. PGU-27A/B TP/ PGU-28A/B SAPHEI / PGU-30A/B TP-T
  2. "Otomatik Orta Kalibre Top". 17 October 2022. Retrieved 17 October 2022.
  3. Williams, Anthony G (January 4, 2021). "Ammunition Data Tables - 20 mm Calibre Cartridges". Military Guns & Ammunition. Solo Publications. Archived from the original on March 30, 2022. Retrieved April 17, 2022.
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