View source for 20 mm caliber

{{Short description|Firearm caliber}}
{{redirect|20mm|the model scale|List of scale model sizes}}
{{refimprove|date=April 2011}}
'''20 mm caliber''' is a specific size of popular [[autocannon]] ammunition. The dividing line between smaller-caliber weapons, commonly called "[[small arm|gun]]s", from larger-caliber "[[cannon]]s" (e.g. [[machine gun]] vs. [[autocannon]]), is conventionally taken to be the 20 mm round, the smallest caliber of autocannon. All 20&nbsp;mm [[cartridge (firearms)|cartridges]] have an outside [[projectile]] ([[bullet]]) diameter and [[gun barrel|barrel]] bore diameter of approximately {{convert|0.787|in|mm}}. These projectiles are typically {{convert|75|to(-)|127|mm|in|sigfig=1|abbr=on}} long, cartridge cases are typically {{convert|75|to(-)|152|mm|in|sigfig=1|abbr=on}} long, and most are [[shell (projectile)|shells]], with an explosive payload and detonating [[fuze]].

Weapons using this caliber range from [[anti-materiel rifle]]s and [[anti-tank rifles]] to aircraft autocannons and [[anti-aircraft warfare|anti-aircraft guns]].

==Usage==
[[File:50BMG size comparison.JPG|thumb|A 20×102&nbsp;mm round (second from left) with .[[50 BMG]] rounds, golf ball, and a stick of 168-pin [[Synchronous dynamic random-access memory|SDRAM]] computer memory]]

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 shell|High explosive]] (HE)
*[[High explosive incendiary]] (HEI)
*[[Armor-piercing shot and shell|Armor-piercing]] (AP)
*[[High Explosive Incendiary/Armor Piercing Ammunition|Semi-armor-piercing high explosive incendiary]] (SAPHEI)
*[[Armour-piercing discarding sabot]] (APDS)
*High explosive fragmentation tracer (HEF-T)
*[[Mine shell|High explosive high capacity]] (HE-M)
*Penetrator with enhanced lateral effect (PELE)
*Target practice - inert projectile (i.e., PGU-27A/B)<ref>
[http://www.globalsecurity.org/military/systems/munitions/pgu-28.htm 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===
{| class="wikitable"
|+
!Weapon
!Country of origin
!Cartridge
!Notes
|-
|[[Neopup PAW-20]]
|{{flag|South Africa}}
|[[20×42mm|20×42&nbsp;mm]]
|
|-
|[[Denel NTW-20]]
|{{flag|South Africa}}
| rowspan="3" |20×82&nbsp;mm Mauser
|
|-
|[[Vektor GA-1|Denel Vektor GA-1]]
|{{flag|South Africa}}
|
|-
|[[Vidhwansak]]
|{{flag|India}}
|
|-
|[[Anzio 20mm rifle]]
|{{flag|United States}}
| rowspan="10" |20×102&nbsp;mm
|
|-
|[[Arash anti-materiel rifle]]
|{{flag|Iran}}
|
|-
|[[M61 Vulcan]]
|{{flag|United States}}
|
|-
|[[M197 electric cannon]]
|{{flag|United States}}
|
|-
|[[M39 cannon]]
|{{flag|United States}}
|
|-
|[[GIAT]] [[M621 cannon|M621]]
|{{flag|France}}
|
|-
|ZVI PL-20 Plamen
|{{flag|Czech Republic}}
|
|-
|[[Nexter]] [[Nexter Narwhal|Narwhal 20A]]
|{{flag|France}}
|Based on the [[M621 cannon|M621]]
|-
|Şahi 20-102
|{{flag|Turkey}}
|<ref>{{Cite web |date=17 October 2022 |title=Otomatik Orta Kalibre Top |url=https://urbansavunma.com.tr/sahi-20/ |access-date=17 October 2022}}</ref>
|-
|[[XM301]]
|{{flag|United States}}
|
|-
|[[Denel NTW-20]]
|{{flag|South Africa}}
| rowspan="4" |20×110&nbsp;mm Hispano
|
|-
|[[RT-20 (rifle)|Metallic RT-20]]
|{{flag|Croatia}}
|
|-
|[[Truvelo Armoury|Truvelo]] CMS 20x110mm
|{{flag|South Africa}}
|
|-
|[[Yugoimport SDPR|Yugoimport-SDPR]] M71/08
|{{flag|Serbia}}
|Single barrel development of [[Zastava M55]]
|-
|[[Oerlikon Contraves|Oerlikon]] KAE (KAA/KAB)
|{{flag|Switzerland}}
| rowspan="2" |20×128&nbsp;mm
|Formerly known as Oerlikon 204GK/5TG
|-
|[[Meroka CIWS]]
|{{flag|Spain}}
|
|-
|[[Hispano-Suiza_HS.820|Oerlikon KAD]]
|{{flag|Switzerland}}
| rowspan="5" |20×139&nbsp;mm
|Formerly known as Hispano-Suiza HS.820
|-
|[[GIAT]] [[20 mm modèle F2 gun|M693/20&nbsp;mm modèle F2]]
|{{flag|France}}
|
|-
|[[Rheinmetall Rh 202]]
|{{flag|Germany}}
|
|-
|[[Denel Land Systems GI-2]]
|{{flag|South Africa}}
|
|-
|[[Nexter]] [[Nexter Narwhal|Narwhal 20B]]
|{{flag|France}}
|Based on the [[20 mm modèle F2 gun|20&nbsp;mm F2]]
|}

===Historical weapons===
{| class="wikitable"
! Weapon
! Country of origin
! Cartridge
! Notes
|-
| [[Becker Type M2 20 mm cannon]]
| {{flag|German Empire}}
| 20×70&nbsp;mm&nbsp;RB
| 
|-
| [[Oerlikon FF]]
| {{CHE}}
| rowspan="2" | 20×72&nbsp;mm&nbsp;RB
| 
|-
| [[Type 99 cannon]], model 1
| {{JPN}}
| 
|-
| Ikaria-Werke Berlin [[MG FF cannon|MG FF/M cannon]]
| {{flag|Nazi Germany}}
| 20×80&nbsp;mm&nbsp;RB
| 
|-
| [[Mauser MG 151/20]]
| {{flag|Nazi Germany}}
| 20×82&nbsp;mm
| 
|-
| [[Ho-5 cannon]]
| {{flag|Japanese Empire}}
| 20×94&nbsp;mm
| 
|-
| [[Berezin B-20]]
| {{flag|Soviet Union}}
| rowspan="3" |20×99&nbsp;mm R<ref>{{cite web |url=http://www.quarryhs.co.uk/ammotable2.html |title=Ammunition Data Tables - 20 mm Calibre Cartridges |last=Williams |first=Anthony G |date=January 4, 2021 |website=Military Guns & Ammunition  |publisher=Solo Publications |access-date=April 17, 2022 |archive-url=https://web.archive.org/web/20220330003338/http://www.quarryhs.co.uk/ammotable2.html |archive-date=March 30, 2022}}</ref>
| 
|-
| [[ShVAK]]
| {{flag|Soviet Union}}
| 
|-
| [[Helenius RK-20]] APH
| {{flag|Finland}}
| Derivative of the [[Helenius RK-97]] 12.7&nbsp;mm anti-materiel rifle
|-
| Ghan-Krnka fortress rifle
| {{flag|Russian Empire}}
| 20.3×95&nbsp;mm&nbsp;R
| Bullet diameter 21&nbsp;mm
|-
| [[Type 99 cannon]], model 2
| class=nowrap|{{flag|Japanese Empire}}
| 20×101&nbsp;mm&nbsp;RB
| 
|-
| [[Solothurn S-18/100]]
| {{CHE}}
| 20×105&nbsp;mm&nbsp;B
| 
|-
| Automatkanon m/45
| {{SWE}}
| rowspan="3" | 20×110&nbsp;mm
| Aircraft [[autocannon]]
|-
| Automatkanon m/49
| {{SWE}}
| Aircraft [[autocannon]]
|-
| class=nowrap|[[Hispano-Suiza HS.404]] and derivatives
| {{CHE}}
| 
|-
| [[Oerlikon 20 mm cannon|Oerlikon F, FFL]]
| {{CHE}}
| 20×110&nbsp;mm&nbsp;RB
| 
|-
| [[Polsten]]
| {{POL}}
| 20×110&nbsp;mm&nbsp;RB
| 
|-
| [[Colt's Manufacturing Company|Colt]] [[Colt Mk 12 cannon|Mk 12 cannon]]
| {{USA}}
|[[20×110mm USN|20×110&nbsp;mm&nbsp;USN]]
| Advanced derivative of the HS.404
|-
| [[Madsen 20 mm anti-aircraft cannon]]
| {{DEN}}
| 20×120&nbsp;mm
| 
|-
| [[Type 97 automatic cannon]]
| {{flag|Japanese Empire}}
| 20×124&nbsp;mm
| 
|-
| [[Mauser MG 213]]
| {{flag|Nazi Germany}}
| 20×135&nbsp;mm
| 
|-
|[[Solothurn S-18/1000]] anti-tank rifle
|{{flag|Switzerland}}
| rowspan="12" |[[20×138mmB|20×138&nbsp;mm&nbsp;B]]
|
|-
|[[Solothurn S-18/1100]] anti-tank rifle
|{{flag|Switzerland}}
|
|-
|[[Solothurn ST-5|ST-5 20 mm]] AA gun
|{{flag|Switzerland}}
|
|-
|[[2 cm FlaK 30|FlaK 30]] and [[2_cm_Flak_30,_Flak_38_and_Flakvierling_38#2,0cm_Flakvierling_38|FlaK 38]] single-barrel AA
|{{flag|Nazi Germany}}
| Forerunner of Hispano-Suiza HS.820's post-war 20×139&nbsp;mm round
|-
|[[2 cm Flak 30/38/Flakvierling#2 cm Flakvierling 38|''Flakvierling'']] quadruple-barrel AA
|{{flag|Nazi Germany}}
|
|-
|[[2_cm_Flak_30,_Flak_38_and_Flakvierling_38#Development|MG C/30L]] aircraft gun
|{{flag|Nazi Germany}}
|
|-
|Rheinmetall [[2 cm KwK 30|KwK 30]] and [[2 cm KwK 30|KwK 38]]
|{{flag|Nazi Germany}}
|
|-
|[[Cannone-Mitragliera da 20/65 modello 35 (Breda)]] 
|{{flag|Kingdom of Italy}}
|
|-
|[[Cannone-Mitragliera da 20/77 (Scotti)]]
|{{flag|Kingdom of Italy}}
|
|-
|[[Lahti L-39]] anti-tank rifle
|{{flag|Finland}}
| Solothurn Long
|-
|[[20 ITK 40 VKT|Lahti L-40]] anti-aircraft gun
|{{flag|Finland}}
|
|-
|[[Nkm wz.38 FK]] anti-tank vehicle-mounted gun
|{{flag|Poland}}
| 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]]
| {{JPN}}
| 20×142&nbsp;mm
|
|-
| [[M/40 Automatic cannon|Automatkanon m/40]]
| {{SWE}}
| 20×145&nbsp;mm&nbsp;R
| [[Autocannon]]
|-
| [[Carl_Gustaf_20mm_recoilless_rifle|Pansarvärnsgevär m/42]]
| {{SWE}}
| 20×180&nbsp;mm&nbsp;R
| [[Recoilless rifle|Recoilless anti-tank rifle]]
|}

== Cartridges ==
(incomplete list)
{| class="wikitable sortable" ="font-size: 9pt; width:750px; text-align:center"
|-
! Dimensions !! Name 
! Date || data-sort-type="number" |Bullet diameter || Case length || data-sort-type="number"|Rim || data-sort-type="number"|Base || Shoulder || data-sort-type="number"| Neck || Cartridge length
|-
| [[20.3х95R Ghan]] 
| || 21 (.827) || 95 (3.74) || - || - || - || - || -
|-
| [[20х150R]] 
| || data-sort-value="21" |~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, 20×102&nbsp;mm is a 20&nbsp;mm projectile in a 102&nbsp;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&nbsp;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&nbsp;mm might be distinguished as ''20×110&nbsp;mm&nbsp;Hispano'', ''20×110&nbsp;mm&nbsp;RB'' and ''20×110&nbsp;mm&nbsp;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==
{{Reflist}}

==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]
*[https://web.archive.org/web/20141109220010/http://www.quarryhs.co.uk/ammotable2.htm Rapid Fire: 20 mm Cartridge Data Table]
*[http://www.quarryhs.co.uk/ATR2.jpg Rapid Fire: 20 mm Antitank Rifle Cartridges image]
*[http://www.quarryhs.co.uk/20mm1.jpg Rapid Fire: 20 mm Autocannon Cartridges WWII image 1]
*[http://www.quarryhs.co.uk/20mm2.jpg Rapid Fire: 20 mm Autocannon Cartridges WWII image 2]
*[http://www.quarryhs.co.uk/20mm3.jpg Rapid Fire: 20 mm Autocannon Cartridges Post-WWII image]

{{Firearm cartridge calibers}}

[[Category:20mm sniper rifles]]
[[Category:Large-caliber cartridges]]
[[Category:Anti-materiel cartridges]]