20 mm caliber is a specific size of popular

autocannon An autocannon, automatic cannon or machine cannon is a automatic firearm, fully automatic gun that is capable of rapid-firing large-caliber ( or more) armour-piercing, explosive or incendiary ammunition, incendiary shell (projectile), shells, ...

ammunition. The dividing line between smaller-caliber weapons, commonly called "

gun A gun is a device that Propulsion, propels a projectile using pressure or explosive force. The projectiles are typically solid, but can also be pressurized liquid (e.g. in water guns or water cannon, cannons), or gas (e.g. light-gas gun). So ...

s", from larger-caliber "

cannon A cannon is a large-caliber gun classified as a type of artillery, which usually launches a projectile using explosive chemical propellant. Gunpowder ("black powder") was the primary propellant before the invention of smokeless powder during th ...

s" (e.g. machine gun vs.

), is conventionally taken to be the 20 mm round, the smallest caliber of autocannon. All 20 mm cartridges have an outside

projectile A projectile is an object that is propelled by the application of an external force and then moves freely under the influence of gravity and air resistance. Although any objects in motion through space are projectiles, they are commonly found ...

(

bullet A bullet is a kinetic projectile, a component of firearm ammunition that is shot from a gun barrel. They are made of a variety of materials, such as copper, lead, steel, polymer, rubber and even wax; and are made in various shapes and constru ...

) diameter and

barrel A barrel or cask is a hollow cylindrical container with a bulging center, longer than it is wide. They are traditionally made of wooden stave (wood), staves and bound by wooden or metal hoops. The word vat is often used for large containers ...

bore diameter of approximately . These projectiles are typically long, cartridge cases are typically long, and most are shells, with an explosive payload and detonating

fuze In military munitions, a fuze (sometimes fuse) is the part of the device that initiates its function. In some applications, such as torpedoes, a fuze may be identified by function as the exploder. The relative complexity of even the earliest fu ...

. Weapons using this caliber range from

anti-materiel rifle An anti-materiel rifle (AMR) is a rifle designed for use against military equipment, structures, and other hardware (materiel) targets. Anti-materiel rifles are chambered in significantly larger calibers than conventional rifles and are employed ...

s and anti-tank rifles to aircraft autocannons and

anti-aircraft guns Anti-aircraft warfare (AAW) is the counter to aerial warfare and includes "all measures designed to nullify or reduce the effectiveness of hostile air action".AAP-6 It encompasses surface-based, subsurface ( submarine-launched), and air-bas ...

Usage

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

Types of ammunition

High explosive An explosive (or explosive material) is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An exp ...

(HE) *

High explosive incendiary In warfare, high-explosive incendiary (HEI) is a type of ammunition specially designed to impart energy and therefore damage to its target in one or both of two ways: via a high-explosive charge and/or via its incendiary (fire-causing) effects. E ...

(HEI) *

Armor-piercing Armour-piercing ammunition (AP) is a type of projectile designed to penetrate armour protection, most often including naval armour, body armour, and vehicle armour. The first, major application of armour-piercing projectiles was to defeat the ...

(AP) * Semi-armor-piercing high explosive incendiary (SAPHEI) *

Armour-piercing discarding sabot Armor-piercing discarding sabot (APDS) is a type of Rifling, spin-stabilized kinetic energy penetrator, kinetic energy projectile for anti-armor warfare. Each projectile consists of a sub-caliber round fitted with a Sabot (firearms), sabot. The co ...

(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

Cartridges

(incomplete list)

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.

References

External links

ATK 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
{{Firearm cartridge calibers 20mm sniper rifles Large-caliber cartridges Anti-materiel cartridges