20 mm caliber

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 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 and PTRD.

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).

Usage

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.

Types of ammunition

* High Explosive
* Armour Piercing
* Armour Piercing Incendiary
* Discarding Sabot Armour Piercing

20 mm weapons

Each weapon is listed with its cartridge type appended.

Current weapons

* RT-20 bolt-action rifle: 20x110
* M61 Vulcan: 20x102
* M197 Gatling gun 20x102
* Oerlikon KAA: 20x128
* Rheinmetall MK 20 Rh202: 20x139
* Denel NTW-20: 20x83.5 and 20x110 [http://www.denellandsystems.co.za/ntw_20_infantry_products.html]

Historical weapons

* Hispano-Suiza HS.404: 20x110
* Hispano-Suiza HS.804: 20x110
* Lahti L-39: 20x138 Solothurn Long
* Mauser MG 213: 20x135
* M39: 20x102
* Oerlikon FF: 20x72RB
* Mauser MG 151/20: 20x82
* Oerlikon F, FFL: 20x100RB
* ShVAK: 20x99R

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.

ee also

* caliber
* .50 BMG
* 14.5 x 114 mm
* 25 mm caliber
* 30 mm caliber
* autocannon
* cannon

External links

* [http://www.fas.org/man/dod-101/sys/land/20mm.htm FAS: 20 mm Cannon Ammunition]
* [http://www.atk.com/customer_solutions_internationalproducts/cs_ip_ma_m-c.asp ATK produced 20, 25 & 30 mm caliber ammunition]
* [http://www.quarry.nildram.co.uk/ammotable2.htm Rapid Fire: 20 mm Cartridge Data Table]
* [http://www.quarry.nildram.co.uk/ATR2.jpgRapid Fire: 20 mm Antitank Rifle Cartridges image]
* [http://www.quarry.nildram.co.uk/20mm1.jpgRapid Fire: 20 mm Autocannon Cartridges WWII image 1]
* [http://www.quarry.nildram.co.uk/20mm2.jpgRapid Fire: 20 mm Autocannon Cartridges WWII image 2]
* [http://www.quarry.nildram.co.uk/20mm3.jpgRapid Fire: 20 mm Autocannon Cartridges Post-WWII image]