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The 20 mm is a specific size of cannon or autocannon ammunition.

Few weapons (aside from shotguns, large game hunting rifles, and heavy caliber muzzleloading "rampart" or "wall guns" popular in the early to mid 19th century European militaries[1]) have been built to fire projectiles between 12.7mm (such as the 12.7mm NATO) and 20 mm, though several 13mm, 14.5mm, and 15mm heavy machine guns were used during World War II, such as the MG 131. The 14.5 mm is still used by some Soviet machine guns, such as the KPV, and anti-tank rifles, such as PTRS, PTRD, and NTW-20. 15mm was also widely used by the Germans during WWII such as in the MG 151, and the British as well to a lesser extent in the 15mm version of the Besa machine gun, which was used on armored cars and some light tanks.

Since 20mm is the cutoff point where most nations switch from bullets to shells, it has come to also generally be the cutoff point between weapons classified as a machine gun or a cannon. This varies, however. For example, in World War II, Japan classified any weapon over 11 mm as a cannon; thus, in Japanese records, their 12.7 mm Ho-103 aircraft gun is classified as an autocannon, as it used explosive shells to overcome its lower muzzle velocity compared to American 12.7mm/.50BMG weapons. A machine gun does not fire shells, so historically a weapon that fires shells below 20 mm can be a cannon. An accurate description always mentions, in addition to caliber, whether the weapon fires bullets or shells.

A small number of anti-tank rifles were produced in 20 mm and larger calibers.

20 mm cartridges have an outside bullet diameter and inside barrel diameter of 0.787 inches (20.0 mm). Projectiles or bullets are typically 75 to 127 mm (3–5 in) long. Cartridge cases are typically 75 to 152 mm (3–6 in) long. Many but not all 20 mm rounds have an explosive filling and detonating fuze.

As an example, the RT-20 sniper rifle fires a 20×110mm 130-gram[2] projectile at a muzzle velocity of 850 m/s.[3] For a simple slug this gives a muzzle energy of 47 kilojoules.

UsageEdit

 
20×102mm round with .50 BMG rounds, golf ball, and a stick of SDRAM computer memory.

Like most cannon ammunition, armed forces typically use 20 mm caliber weapons against large targets, such as vehicles, buildings, or aircraft. Though lethal against individual soldiers, 20mm ammunition is so large and heavy that its effects are inefficient against relatively small targets.

Types of ammunitionEdit

20 mm weaponsEdit

Each weapon is listed with its cartridge type appended.

Current weaponsEdit

Weapon Country of origin Cartridge Notes
Neopup PAW-20   South Africa 20×42mm
Denel NTW-20   South Africa 20×82mm Mauser
Vidhwansak   India
Anzio 20mm rifle   United States 20×102mm
M61 Vulcan   United States
M197 electric cannon   United States
M39 cannon   United States
GIAT M621   France
ZVI PL-20 Plamen   Czech Republic
Metallic RT-20   Croatia 20×110mm Hispano
Oerlikon 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
Rheinmetall Rh 202   Germany
Denel Land Systems GI-2   South Africa

Historical weaponsEdit

Weapon Country of origin Cartridge Notes
Ghan-Krnka fortress rifle   Russian Empire 20,3×95mm R Bullet diameter 21 mm
Type 99 cannon, model 2   Japanese Empire 20×101mm RB
Solothurn S-18/100    Switzerland 20×105mm B
Bofors m/45   Sweden 20×110mm
Bofors m/49   Sweden
Hispano-Suiza HS.404 and derivatives    Switzerland
Oerlikon F, FFL    Switzerland 20×110mm RB
Polsten   Poland 20×110mm RB
Colt Mk 12 cannon   United States 20×110mm USN Advanced derivative of the HS.404
Madsen 20 mm anti-aircraft cannon   Denmark 20×120mm
Type 97 automatic cannon   Japanese Empire 20×124mm
Mauser MG 213   Nazi Germany 20×135mm
Breda Model 35   Kingdom of Italy 20×138mm B
Nkm wz.38 FK   Poland Designated "Heaviest Machine Gun", or "Najciezszy karabin maszynowy, Nkm," AA/AT (actually an autocannon)
Rheinmetall 2 cm KwK 30   Nazi Germany
Scotti 20 mm   Kingdom of Italy
Solothurn S-18/1000 Long    Switzerland
FlaK 38   Nazi Germany Forerunner of Hispano-Suiza HS.820's post-war 20×139mm round
Lahti L-39   Finland Solothurn Long
Bofors m/40   Sweden 20×145mm R
Becker Type M2 20 mm cannon   German Empire 20×70mm RB
Oerlikon FF    Switzerland 20×72mm RB
Type 99 cannon, model 1   Japan
Ikaria-Werke Berlin MG FF/M cannon   Nazi Germany 20×80mm RB
Mauser MG 151/20   Nazi Germany 20×82mm
Ho-5 cannon   Japanese Empire 20×94mm
Berezin B-20   Soviet Union 20×99mm
ShVAK   Soviet Union 20×99mm R

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.

See alsoEdit

ReferencesEdit

  1. ^ Editor. "Big Shots – Amusettes, Jingals And Other Super-Sized Firearms | Militaryhistorynow.com". Retrieved 2016-03-28.
  2. ^ Williams, A.G. & Gustin, E. (2009): World War 2 fighter armament effectiveness.
  3. ^ *RT-20 on World Guns.ru Archived 2006-04-27 at the Wayback Machine
  4. ^ PGU-27A/B TP/ PGU-28A/B SAPHEI / PGU-30A/B TP-T

External linksEdit