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The 20 mm caliber is a specific size of cannon or autocannon ammunition, commonly the smallest caliber which is unambiguously a cannon (or more commonly today, autocannon) and not a heavy machine gun.

There are relatively few weapons (aside from shotguns and large game hunting rifles) which have been built which fire projectiles between .50 caliber (0.50 inch/12.7 mm, roughly 12 mm caliber) and 20 mm caliber, though the 14.5 mm caliber was 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 up calibers.

20 mm caliber cartridges have an outside shell diameter and inside barrel diameter of 0.8 inch (20 millimeters). Projectiles or shells are typically 75-100 mm (3-4 inches) long. Cartridges are typically 75-125 mm (3-5 inches) 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 1,035 m/s (3395 ft/s). For a simple slug round this is a muzzle energy of 53,600 joules (or 39,500 ft·lbf).

[edit] Usage

20 mm with .50 BMG rounds, golf ball, stick of RAM.

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

[edit] Types of ammunition

• High Explosive (HE)
• High Explosive Incendiary (HEI)
• Armour Piercing (AP)
• Armour Piercing Incendiary (API)
• Discarding Sabot Armour Piercing or proper APDS
• Target Practice- Inert projectile. Used for training. (TP)
• Target Practice Tracer- Inert projectile with tracer material in base for visual trajectory tracking. (TPT)

[edit] 20 mm weapons

Each weapon is listed with its cartridge type appended.

[edit] Current weapons

• Denel NTW-20: 20×82mm Mauser or 20×110mm Hispano caliber
• GIAT M621: 20×102mm
• M61 Vulcan: 20×102mm
• M197 Gatling gun: 20×102mm
• Pontiac M39: 20×102mm
• RT-20 bolt-action rifle: 20×110mm
• 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: 20×139mm
• Rheinmetall MK 20 Rh 202: 20×139mm
• Vidhwansak Indian Anti-Material rifle

[edit] Historical weapons

• Hispano-Suiza HS.404: 20×110mm
• Hispano-Suiza HS.804: 20×110mm
• Lahti L-39: 20×138mm (Solothurn Long)
• Rheinmetall FlaK 38: 20×138mm forerunner of Hispano-Suiza HS.820 post-war 20×139mm round
• Mauser MG 213: 20×135mm
• Oerlikon FF: 20×72mm RB
• MG FF/M cannon: 20×80mm
• Mauser MG 151/20: 20×82mm
• Oerlikon F, FFL: 20×100mm RB
• ShVAK: 20×99mm R
• Solothurn S-18/100: 20×105mm B
• Solothurn S-18/1000: 20×138mm

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.

[edit] See also

• caliber
• .50 BMG
• 14.5 × 114 mm
• 23 × 115 mm
• 23 × 152 mm
• 25 mm caliber
• 30 mm caliber
• autocannon
• cannon

[edit] 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