20 mm Caliber

20 mm caliber is a specific size of popular autocannon ammunition. It is typically used to distinguish smaller-caliber weapons, commonly called " guns", from larger-caliber " cannons" (e.g. machine gun vs. autocannon). All 20 mm cartridges have an outside projectile (bullet) diameter and barrel bore diameter of . These projectiles are typically long, cartridge cases are typically long, and most are shells, with an explosive payload and detonating fuze.

Weapons using this caliber range from anti-materiel rifles and anti-tank rifles to aircraft autocannons and anti-aircraft guns.

Usage

Twenty-millimeter-caliber weapons are generally not used to target individual soldiers, but have targets such as vehicles, buildings, or aircraft.

Types of ammunition

* High explosive (HE)
* High explosive incendiary (HEI)
* Armor-piercing (AP)
* Semi-armor-piercing high explosive incendiary (SAPHEI)
* Armor-piercing discarding sabot (APDS)
*High explosive fragmentation tracer (HEF-T)
* High explosive high capacity (HE-M)
*Penetrator with enhanced lateral effect (PELE)
*Target practice - inert projectile (i.e., PGU-27A/B)PGU-27A/B TP/ PGU-28A/B SAPHEI / PGU-30A/B TP-T
/ref> 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

Historical weapons

Naming conventions

The usual nomenclature of ammunition indicates the diameter of projectile and the length of the cartridge that holds it; for example, 20×102 mm is a 20 mm projectile in a 102 mm long case.

Though this designation is often assumed to be unique, this is not always the case, e.g. there are three different 20×110 mm types which are not compatible. These may be distinguished in that some cartridge designations may include additional letters or names as a suffix, e.g. the various different types of 20×110 mm might be distinguished as ''20×110 mm Hispano'', ''20×110 mm RB'' and ''20×110 mm USN''.

Common suffixes

* B e.g. 20×138''B'': the cartridge has a belt which is used for headspacing, i.e. it helps ensure the correct positioning within the gun's chamber.
* R e.g. 20×145''R'': a rimmed cartridge: the diameter of the rim forming the base is larger than that of the cartridge case itself.
* RB e.g. Oerlikon 20×110''RB'': rebated rim, one where the rim is a smaller diameter than the case head allowing the extractor to follow it into the chamber, facilitating advanced-primer ignition, a recoil-moderating system.

See also

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

References

{{Reflist

External links

FAS: 20 mm Cannon AmmunitionATK produced 20, 25 & 30 mm caliber ammunitionRapid Fire: 20 mm Antitank Rifle Cartridges imageRapid Fire: 20 mm Autocannon Cartridges WWII image 1Rapid Fire: 20 mm Autocannon Cartridges WWII image 2Rapid Fire: 20 mm Autocannon Cartridges Post-WWII image

20mm sniper rifles
Large-caliber cartridges