The 20×110mm USN (also known as 20×110mm US Navy and 20mm Mk-100 Series) is an autocannon cartridge developed by the US Navy after World War II for use in Mk 11 and Mk 12autocannons. They are called the Mk 100 series as they range from Mk 101 to Mk 109.
It has the same rim diameter as the 20×102mm but a different length and contour. It is not interchangeable with any other 20×110mm cartridge.[1]
Available loads
Some of the available loads for the 20×110mm USN are as follows:
Name
Pressure (PSI)
Projectile weight (grains)
Projectile Type
Muzzle Velocity (fps)
Identification
Cartridge, 20 mm, high pressure test, Mk 101 Mod 0 (USN)
Not to exceed 72,500
1700
Inert
Not listed
Green or blue projectile with brown nose and 1/4 black letters reading "High pressure test round"
Cartridge, 20 mm, low pressure test, Mk 102 Mod 0 (USN)
Not listed
1700
Inert
Not listed
Green or blue projectile with brown nose and 1/4 black letters reading "Low pressure test round"
Cartridge, 20 mm, high explosive incendiary, Mk 105 Mod 0 (USN)
Not to exceed 72,500
1700
Inert
3350
Green or blue projectile black lettering or blue projectile with brown nose and black lettering
Cartridge, 20 mm, high explosive incendiary, Mk 106 Mod 0 & 1 (USN)
60,000
1700 ±50
Impact detonating
3350
Unpainted fuze, red and yellow projectile
Cartridge, 20 mm, armor-piercing incendiary, Mk 107 Mod 0 (USN)
60,000
1700 ±50
Armor-piercing incendiary
3350
No fuze, nose of projectile blue or brown with red band. Body of projectile black with white lettering.
Cartridge, 20 mm, armor-piercing tracer, Mk 108 Mod 0 (USN)
60,000
1700 ±50
Armor-piercing tracer
3350
No fuze. Hollow windshield. Brown or yellow nose, body of projectile black with white lettering.
There is also a cartridge, 20 mm, dummy, Mk 103 Mod 0 (USN) which is an inert round. It has an empty primer pocket and holes in the case or a plugged primer pocket. It may be empty or filled with inert material. The projectile is usually brass or bronze plated.[2]
References
^Albert Watson III (1985). Small Calibre Ammunition Identification Guide, DST-1160G-514-82-VOL 2-CHG 1(Volume 2: 20mm to 40mm Cartridges.). Defence Intelligence Agency.
