20 mm caliber

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

There are few weapons (aside from shotguns and large game hunting rifles) which have been built that fire projectiles between .50 caliber (0.50 in, roughly 13 mm caliber) and 20 mm caliber, though the 14.5 mm caliber is used by some Soviet machineguns such as the KPV and antitank rifles such as PTRS, PTRD, and NTW-20.

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

20 mm caliber cartridges have an outside shell diameter and inside barrel diameter of 0.79 in. Projectiles or shells are typically 75 to(-) long. Cartridges are typically 75 to(-) long. Many but not all 20 mm shells have an explosive filling and detonating fuze.

As an example, the 20x102 has a 100 gram bullet fired at a muzzle velocity of 1035 m/s. For a simple slug round this is a muzzle energy of 53567 J.

Usage
Like most cannon ammunition, 20 mm caliber weapons are typically used against large targets such as vehicles, buildings, or aircraft. Though lethal against individual soldiers, 20 mm ammunition is so large and heavy that its effects are inefficiently utilized on such relatively small targets.

Types of ammunition

 * High Explosive (HE)
 * High Explosive Incendiary (HEI)
 * Armour-Piercing (AP)
 * Armour Piercing Incendiary (API)
 * Armour-Piercing Discarding Sabot (APDS)
 * 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

 * Vidhwansak: 20×82mm
 * Anzio 20mm rifle: 20x102mm
 * RT-20 bolt-action rifle: 20×110mm
 * Denel NTW-20: 20×82mm Mauser or 20×110mm Hispano caliber
 * M61 Vulcan: 20×102mm (PGU-28/B)
 * M197 Gatling gun: 20×102mm
 * M39 cannon: 20×102mm
 * GIAT M621: 20×102mm
 * Oerlikon KAA & KAB: 20×128mm (formerly the Oerlikon 204GK and 5TG respectively)
 * Meroka: 20x128mm
 * Oerlikon KAD: 20×139mm (formerly the Hispano-Suiza HS.820)
 * GIAT M693/20 mm modèle F2 gun: 20×139mm
 * Rheinmetall MK 20 Rh 202: 20×139mm
 * Denel Land Systems GI-2: 20×139mm

Historical weapons

 * Bofors M/40: 20x145mm R
 * Bofors M/45: 20x110
 * Bofors M/49: 20x110
 * Colt Mk 12 cannon: 20x110mm USN (Mk 12 is an advanced derivative of the HS.404)
 * Hispano-Suiza HS.404 and derivatives: 20×110mm
 * Hispano-Suiza HS.804: 20×110mm
 * Lahti L-39: 20×138mm B (Solothurn Long)
 * Madsen 20 mm anti-aircraft cannon: 20x120mm
 * Mauser MG 213: 20×135mm
 * MG FF/M cannon: 20×80mm RB
 * Mauser MG 151/20: 20×82mm
 * Nkm wz.38 FK designated: "Heaviest Machinegun" "Hmg" or "Najciezszy karabin maszynowy, Nkm," AA/AT 20x138 mmB autocannon
 * Oerlikon FF: 20×72mm RB
 * Oerlikon F, FFL: 20×110mm RB
 * Rheinmetall FlaK 38: 20×138mm B forerunner of Hispano-Suiza HS.820 post-war 20×139mm round
 * ShVAK: 20×99mm R
 * Solothurn S-18/100: 20×105mm B
 * Solothurn S-18/1000: 20×138mm B
 * Type 99 cannon : 20x72RB
 * Ho-5 cannon : 20x94

Cartridge type indicates the diameter of projectile and the length of the cartridge that holds it, for example 20x102 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.