Bordkanone Rheinmetall BK-5:
This gun is the result of the adaptation of the tank gun Kwk 39/1 to aeronautical use.
Teorically the BK 5 could be used towards any aerial or ground target but his main reason to development was that the five centimeter shell promise the definately destruction of a 4 engined bomber with a single shot in that way it was the "Final solution" against the B-17 and B-24.
The Kwk 39 was used in the Panzer III ausf J, L, M, and the heavy armored car "Puma", also was projected to mount in the recce tank "Leopard" wich never saw service.
The gun was a single shot, 60 calibres long recoil operated hydro pneumatic recuperation system and semiautomatic breech, that means in every shot the entire barrel recoil togheter , in the last mm of the travel back the chamber is opened and extract the used cartrigde cocking the action and leaving this ready to insert the next round. Once the new round is inserted the breech is automatically close and the gun is ready to fire.
The modification suffered to became the BK 5 were:
A) Barrel lenght , the tube was shortened about 0.5 m and provided with a single chamber multiple perforations muzzle brake.
B) Loading; to improve the rate of fire the manual loading was deleted, and a pneumatically assisted system used. The barrel in the recoil movement engaged a series of electric switches and mechanichal levers.
Those were in charge to command a rammer, a extractor and the mechanism to turn closed belt.
This mechanism was in charge to insert the used round back in the belt and to introduce a fresh cartrigde, the gun was fired just a moment after the breech was closed. The 2400kg recoil of the weapon was alleviated by a hydraulic damper.
Compressed air circuits in BK 5.
The feeding was provided by a closed belt of 22 rounds, the rate of fire was 45-50 rpm. Pneumatic power came from 2 big compressed air bottles.
Rammer pushing a shell into the chamber.
The BK 5 was installed in the Me-410, some variants of the JU-88, JU-288 and He-177.
Characteristics:
Operation system: Pneumatically assisted long recoil.
Barrel lenght :2700 mm.
Total lenght :3790 mm.
Weight: 520 kg.
Rate of fire: 45-50 dpm
Ammunition: 50mm x 420R ( KwK 39, Pak 38 )
In Junkers Ju-88P-4 from VII/Kampfgruppe 1, sometimes this gun is mixed up with the larger BK of 75 mm.