Bordkanone Rheinmetall BK-5:
As WW2 progressed , it became clear that existing aircraft guns were too light to effectively combat bombers which were increasingly armoured. Weapons like the 3 cm Mk-108 gun were effective against bombers ; 3 to 5 hits on a heavy bomber were enough to bring it down, however the short range and curved flight path (low velocity) of the Mk-108 projectiles meant the enemy plane had to be approached quite close to ensure –enough- hits. The 3 cm Mk101 gun projectile was much faster and had a flat projectile trajectory, however the rate of fire was much lower (meaning less chance of multiple hits). As most bombers were heavily armed with machine gun turrets this was very risky business. Therefore it was decided to develop a heavier weapon that could fire from a safe distance, and would only need one hit to ensure a shot down enemy bomber; the BK-5.
The BK-5 gun is the result of the adaptation of the tank gun Kwk 39/1 to aeronautical use.
Theoretical the BK-5 could be used towards any aerial or ground target but his main reason to development was that the five centimeter shell promised the definitive destruction of a 4 engined bomber with a single shot.
The Kwk 39 was used in the Panzer III ausf J, L, M, and the heavy armored car "Puma", it was also projected to mount in the recce tank "Leopard" wich never saw service.
The gun is single shot, 60 calibres long, with a recoil operated hydro pneumatic recuperation system and semiautomatic breech, meaning that in the last mm of the recoil the chamber is opened and the spent shellcase is extracted. Once the new round is inserted (manually) the breech automatically closes and the gun is ready to fire.
The modifications from KwK/39 to become the BK-5 were:
A) Barrel length; the barrel was shortened about 0.5 m and provided with a single
chamber multiple perforated muzzle brake.
B) Loading; to improve the rate of fire the manual loading was deleted, and a pneumatically assisted system was added. The barrel in the recoil movement engaged a series of electric switches and mechanichal levers. These were meant to command a rammer, an extractor and the mechanism to turn the closed ammo belt.
The 2400kg recoil of the weapon was alleviated by a hydraulic damper.
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
The BK 5 was installed in the Me-410, the Me-262 A1/U4 some variants of the JU-88, the 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)
Browsing the page Luftwaffe [LuftArchiv.de - Das Archiv der Deutschen Luftwaffe] 2.WK
I have found some interesting information of the use of this weapon in the me-410A-1/U4.
Quote:
”Especially with the use of the 5cm M –shell remarkable results have been made; a group of 53 ME 410 A1/U4 planes -each equipped with a BK-5- has shot down 129 B-17 “flying Fortresses” and 4 B-24 “Liberators” in six flights between 22 Februari and 11 April 1944.
This with a loss of just nine planes on our side. On 9 and 11 April, nine B-17’s were shot down from a plm, 800 mtrs distance. This proves the great value of the BK-5.”
Description of the 5 cm M-granate (M-shell):
The projectile exists of a thin walled drawn steel body, rolled inward at the top.
It is fuzed with the AZ39 (Impact fuze 39), either the ZZ-20 (Zerlege Zunder / Self destruct fuze 20).
The projectile is filled with 335 grams of cast HTA (Hexogen, TNT, Aluminium), and has a 12 grams –cylinder shaped booster charge of NP10 (Nitropenta with 10% wax) below the detonator.
The tracer at the base of the projectile burns dimmed for the first 0,25 seconds (prevents blinding of pilot), followed by 3,3 seconds of bright tracer.
Functioning of the AZ-39 impact fuze:
The AZ-39 is an all aluminium fuze. A slider prevents the firing pin (red) from moving downward. The slider is held in place by two radial placed pins that fall in recesses in the side of the slider. These two pins are held inward by a bronze clock spring. Upon firing these two pins are thrown outward (centrifugal force), releasing the slider. A steel ball is placed in an axial hole that is placed under a 2 degrees outward angle to the top of the fuze. When fired, the negative acceleration keeps the ball in the lower position, as soon as the velocity is constant, the centrifugal force will make the ball creep upward until it falls into the hole in the slider. As the slider becomes heavier on this side it will pull the outward, releasing the firing pin. On impact the firing pin is driven into the upper firing cap (green) of the VC-70 detonator.
This detonator has a delay mechanism build in, delaying the explosion with 10 cm of projectile flight path. This ensures the projectile will explode inside the target instead of “on contact”. When the firing pin (red) hits the firing cap (green) the flame travels through the small channel into the ring formed chamber where it has to pass through another small channel to reach the lower firing cap (yellow). This will activate the detonator (white)
The shellcase used is the 50 x 420R, the same as used in the KwK/39. It is electrically ignited by means of the C/22 igniter. The shellcase is a copper clad steel shellcase.
The powder charge exists of 830 grams Digl.R.P. 310 x 2,5 x 1,0 (hole) powder sticks and a booster charge of 10 grams NZ.Man. Nd.P 1,5 x 1,5, placed below the main powder charge.
The powder sticks are placed in a silk bag and held together with to silk wires.
The maximal barrel pressure is 2400 Bar (At)
Vo. of the projectile : 920 mtrs/sec
Weight of complete cartridge : 3500 plm. 40 grams
Weight of projectile : 1520 plm. 20 grams
Length of the complete cartridge : 606 mm
Length of the projectile : 226,5 mm
Regards , DJH
As WW2 progressed , it became clear that existing aircraft guns were too light to effectively combat bombers which were increasingly armoured. Weapons like the 3 cm Mk-108 gun were effective against bombers ; 3 to 5 hits on a heavy bomber were enough to bring it down, however the short range and curved flight path (low velocity) of the Mk-108 projectiles meant the enemy plane had to be approached quite close to ensure –enough- hits. The 3 cm Mk101 gun projectile was much faster and had a flat projectile trajectory, however the rate of fire was much lower (meaning less chance of multiple hits). As most bombers were heavily armed with machine gun turrets this was very risky business. Therefore it was decided to develop a heavier weapon that could fire from a safe distance, and would only need one hit to ensure a shot down enemy bomber; the BK-5.
The BK-5 gun is the result of the adaptation of the tank gun Kwk 39/1 to aeronautical use.
Theoretical the BK-5 could be used towards any aerial or ground target but his main reason to development was that the five centimeter shell promised the definitive destruction of a 4 engined bomber with a single shot.
The Kwk 39 was used in the Panzer III ausf J, L, M, and the heavy armored car "Puma", it was also projected to mount in the recce tank "Leopard" wich never saw service.
The gun is single shot, 60 calibres long, with a recoil operated hydro pneumatic recuperation system and semiautomatic breech, meaning that in the last mm of the recoil the chamber is opened and the spent shellcase is extracted. Once the new round is inserted (manually) the breech automatically closes and the gun is ready to fire.
The modifications from KwK/39 to become the BK-5 were:
A) Barrel length; the barrel was shortened about 0.5 m and provided with a single
chamber multiple perforated muzzle brake.
B) Loading; to improve the rate of fire the manual loading was deleted, and a pneumatically assisted system was added. The barrel in the recoil movement engaged a series of electric switches and mechanichal levers. These were meant to command a rammer, an extractor and the mechanism to turn the closed ammo belt.
The 2400kg recoil of the weapon was alleviated by a hydraulic damper.
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
The BK 5 was installed in the Me-410, the Me-262 A1/U4 some variants of the JU-88, the 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)
Browsing the page Luftwaffe [LuftArchiv.de - Das Archiv der Deutschen Luftwaffe] 2.WK
I have found some interesting information of the use of this weapon in the me-410A-1/U4.
Quote:
”Especially with the use of the 5cm M –shell remarkable results have been made; a group of 53 ME 410 A1/U4 planes -each equipped with a BK-5- has shot down 129 B-17 “flying Fortresses” and 4 B-24 “Liberators” in six flights between 22 Februari and 11 April 1944.
This with a loss of just nine planes on our side. On 9 and 11 April, nine B-17’s were shot down from a plm, 800 mtrs distance. This proves the great value of the BK-5.”
Description of the 5 cm M-granate (M-shell):
The projectile exists of a thin walled drawn steel body, rolled inward at the top.
It is fuzed with the AZ39 (Impact fuze 39), either the ZZ-20 (Zerlege Zunder / Self destruct fuze 20).
The projectile is filled with 335 grams of cast HTA (Hexogen, TNT, Aluminium), and has a 12 grams –cylinder shaped booster charge of NP10 (Nitropenta with 10% wax) below the detonator.
The tracer at the base of the projectile burns dimmed for the first 0,25 seconds (prevents blinding of pilot), followed by 3,3 seconds of bright tracer.
Functioning of the AZ-39 impact fuze:
The AZ-39 is an all aluminium fuze. A slider prevents the firing pin (red) from moving downward. The slider is held in place by two radial placed pins that fall in recesses in the side of the slider. These two pins are held inward by a bronze clock spring. Upon firing these two pins are thrown outward (centrifugal force), releasing the slider. A steel ball is placed in an axial hole that is placed under a 2 degrees outward angle to the top of the fuze. When fired, the negative acceleration keeps the ball in the lower position, as soon as the velocity is constant, the centrifugal force will make the ball creep upward until it falls into the hole in the slider. As the slider becomes heavier on this side it will pull the outward, releasing the firing pin. On impact the firing pin is driven into the upper firing cap (green) of the VC-70 detonator.
This detonator has a delay mechanism build in, delaying the explosion with 10 cm of projectile flight path. This ensures the projectile will explode inside the target instead of “on contact”. When the firing pin (red) hits the firing cap (green) the flame travels through the small channel into the ring formed chamber where it has to pass through another small channel to reach the lower firing cap (yellow). This will activate the detonator (white)
The shellcase used is the 50 x 420R, the same as used in the KwK/39. It is electrically ignited by means of the C/22 igniter. The shellcase is a copper clad steel shellcase.
The powder charge exists of 830 grams Digl.R.P. 310 x 2,5 x 1,0 (hole) powder sticks and a booster charge of 10 grams NZ.Man. Nd.P 1,5 x 1,5, placed below the main powder charge.
The powder sticks are placed in a silk bag and held together with to silk wires.
The maximal barrel pressure is 2400 Bar (At)
Vo. of the projectile : 920 mtrs/sec
Weight of complete cartridge : 3500 plm. 40 grams
Weight of projectile : 1520 plm. 20 grams
Length of the complete cartridge : 606 mm
Length of the projectile : 226,5 mm
Regards , DJH
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