20 mm caliber

20 mm caliber is a specific size of popular autocannon ammunition. The dividing line between smaller-caliber weapons, commonly called "guns", from larger-caliber "cannons" (e.g. machine gun vs. autocannon), is conventionally taken to be the 20 mm round, the smallest caliber of autocannon. All 20 mm cartridges have an outside projectile (bullet) diameter and barrel bore diameter of approximately 0.787 inches (20.0 mm). These projectiles are typically 75 to 127 mm (3–5 in) long, cartridge cases are typically 75 to 152 mm (3–6 in) 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.

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

• High explosive (HE)
• High explosive incendiary (HEI)
• Armor-piercing (AP)
• Semi-armor-piercing high explosive incendiary (SAPHEI)
• Armour-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)^[1] 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)

Each weapon is listed with its cartridge type appended.

The usual nomenclature of ammunition indicates the diameter of projectile and the length of the cartridge that holds it; for example, ×ばつ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 ×ばつ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 ×ばつ110 mm might be distinguished as ×ばつ110 mm Hispano, ×ばつ110 mm RB and ×ばつ110 mm USN.

• B e.g. ×ばつ138B: 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. ×ばつ145R: a rimmed cartridge: the diameter of the rim forming the base is larger than that of the cartridge case itself.
• RB e.g. Oerlikon ×ばつ110RB: 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.

• 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

• 20mm sniper rifles
• Large-caliber cartridges
• Anti-materiel cartridges

• Articles with short description
• Short description matches Wikidata
• Articles needing additional references from April 2011
• All articles needing additional references