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 . 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 rather objects 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) 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) 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 +WeaponCountry of originCartridgeNotesNeopup PAW-2020×42mmDenel NTW-2020×82mm MauserDenel Vektor GA-1VidhwansakAnzio 20mm rifle20×102mmArash anti-materiel rifleM61 VulcanM197 electric cannonM39 cannonGIAT M621ZVI PL-20 PlamenNexter Narwhal 20ABased on the M621Şahi 20-102XM301Denel NTW-2020×110mm HispanoMetallic RT-20Truvelo CMS 20x110mmYugoimport-SDPR M71/08Single barrel development of Zastava M55Oerlikon KAE (KAA/KAB)20×128mmFormerly known as Oerlikon 204GK/5TGMeroka CIWS Escribano SENTINEL 20 RWSOerlikon KAD20×139mmFormerly known as Hispano-Suiza HS.820GIAT M693/20 mm modèle F2Rheinmetall Rh 202Denel Land Systems GI-2Nexter Narwhal 20BBased on the 20 mm F2
Historical weapons Weapon Country of origin Cartridge Notes Becker Type M2 20 mm cannon 20×70mmRB Oerlikon FF 20×72mmRB Type 99 cannon, model 1 Ikaria-Werke Berlin MG FF/M cannon 20×80mmRB Mauser MG 151/20 20×82mm Ho-5 cannon 20×94mm Berezin B-20 20×99mmR ShVAK Helenius RK-20 APH Derivative of the Helenius RK-97 12.7 mm anti-materiel rifle Ghan-Krnka fortress rifle 20.3×95mmR Bullet diameter 21 mm Type 99 cannon, model 2 20×101mmRB Solothurn S-18/100 20×105mmB Automatkanon m/45 20×110mm Aircraft autocannon Automatkanon m/49 Aircraft autocannonHispano-Suiza HS.404 and derivatives Oerlikon F, FFL 20×110mmRB Polsten 20×110mmRB Colt Mk 12 cannon 20×110mm USN Advanced derivative of the HS.404 Madsen 20 mm anti-aircraft cannon 20×120mm Type 97 automatic cannon 20×124mm Mauser MG 213 20×135mm Solothurn S-18/1000 anti-tank rifle20×138mmBSolothurn S-18/1100 anti-tank rifleST-5 20 mm AA gunFlaK 30 and FlaK 38 single-barrel AA Forerunner of Hispano-Suiza HS.820's post-war 20×139mm roundFlakvierling quadruple-barrel AAMG C/30L aircraft gunRheinmetall KwK 30 and KwK 38Cannone-Mitragliera da 20/65 modello 35 (Breda) Cannone-Mitragliera da 20/77 (Scotti)Lahti L-39 anti-tank rifle Solothurn LongLahti L-40 anti-aircraft gunNkm wz.38 FK anti-tank vehicle-mounted gun Designated "heaviest machine gun", or "Najcięższy karabin maszynowy, Nkm", AA/AT (actually an autocannon) Type 98 20 mm AA machine cannon and Type 4 20 mm twin AA machine cannon 20×142mm Automatkanon m/40 20×145mmR Autocannon Pansarvärnsgevär m/42 20×180mmR Recoilless anti-tank rifle
Cartridges (incomplete list) Dimensions Name Date Bullet diameter Case length Rim Base Shoulder Neck Cartridge length 20.3×95R Ghan 21 (.827) 95 (3.74) - - - - - 20×150R ~21 (~.827) 150 (5.9) - - - - -
Naming conventions The usual nomenclature of ammunition indicates the diameter of projectile and the length of the cartridge that holds it; for example, 20×102mm 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 20×110mm 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 20×110mm might be distinguished as 20×110mm Hispano, 20×110mmRB and 20×110mm USN.
Common suffixes B e.g. 20×138B: 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. 20×145R: a rimmed cartridge: the diameter of the rim forming the base is larger than that of the cartridge case itself. RB e.g. Oerlikon 20×110RB: 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.
References
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