Thanks!
Digging around, I found this in my Hornet archives ( Translated in english ):
"The gun was approved as a naval armament in November 1940, and the first series appeared on US ships before 7 December 1941. From June 1942, Oerlikon 20mm guns were used as anti-aircraft weapons on the three Yorktown aircraft carriers.The Oerlikon L70 Mk 4 20mm guns had an overall length of 2210m and weighed about 20.87kg without the breech mechanism.
Their barrels were 1452 mm long (70 calibres) and had nine 1/36 thread grooves over a length of 1246 mm, allowing the projectile to rotate at 1154 revolutions per second as it exited the barrel. The volume of the barrel's cartridge chamber was 34.86 cm3 and, with the breech mechanism, they weighed 68 kg. The 20mm guns fired 182mm long combination cartridges weighing 0.241kg. The 0.09kg brass cartridge cases were filled with 0.028kg of nitrocellulose propellant, creating a pressure of 3090kg/cm2 in the cartridge chamber. Depending on the condition of the weapon, the projectiles could reach an exit velocity of 835 to 844 m/s. This gave a range of 4400 metres. This gave a range of 4,400 m at 45o elevation and a ceiling of 3,050 m for anti-aircraft fire. The theoretical rate of fire of the 20mm guns was 450 rounds per minute in cyclic fire, and the practical rate of fire was 250 to 320 rounds per minute. The guns had a service life of 9,000 rounds.
The 20mm L/70Mk 4 Oerlikon anti-aircraft guns were mounted on Yorktown aircraft carriers in Mk 4 and Mk 10 single gun emplacements and Mk 24 double gun emplacements. The single gun emplacement weighed 769 kg and the double gun weighed 635 kg. The elevation angle of the guns could be changed manually using a mechanical lift from -5o to +87o (Mk 4 mounts) or from -15o to +90o (Mk 10 and Mk 24 mounts). In the horizontal plane, the fields of fire could be rotated 360o, and the rotation and alignment of the fields of fire in the direction of the target on single- and double-turret positions was effected by the force of the sighting officer's arms."
I extracted this from here:
OW23 Lotniskowce typu Yorktown vol 1.



