20 mm caliber

"20mm" redirects here. For the model scale, see List of scale model sizes.

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) 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 projectile at a muzzle velocity of 850 m/s. For a simple slug this gives a muzzle energy of 47 kilojoules.

Usage

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 ammunition

• High Explosive (HE)
• High Explosive Incendiary (HEI)
• Armour-Piercing (AP)
• Semi Armour Piercing High Explosive Incendiary (SAPHEI)
• Armour-Piercing Discarding Sabot (APDS)
• High-Explosive Fragmentary tracer (HEF-t)
• Penetrator with Enhanced Lateral Effect (PELE)
• Target Practice - Inert projectile (i.e., PGU-27A/B). 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
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 weapons

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 also

• .50 BMG
• .950 JDJ
• 14.5×114mm
• 20×110mm USN
• 23 mm caliber
  • 23×115mm
  • 23×152mm
• 25 mm caliber
• 30 mm caliber

External links

• FAS: 20 mm Cannon Ammunition
• ATK produced 20, 25 & 30 mm caliber ammunition
• Rapid Fire: 20 mm Cartridge Data Table
• Rapid Fire: 20 mm Antitank Rifle Cartridges image
• Rapid Fire: 20 mm Autocannon Cartridges WWII image 1
• Rapid Fire: 20 mm Autocannon Cartridges WWII image 2
• Rapid Fire: 20 mm Autocannon Cartridges Post-WWII image