Rheinmetall BK-5

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	Weapon: Rheinmetall BK-5 Type: Autocannon Country of Origin: Germany Year Adopted: 1944 Caliber: 50x420mmR Action: Revolver Cannon Overall Length (mm): 4348.0 Overall Length (in): 171.18 Weight (kg): 540.00 Weight (pounds): 1190.5 Effective Range (m): 1500 m Effective Range (yards): 1640.42

The Rheinmetall BK-5 (Bordkanone 5) was a powerful 50mm autocannon developed by Germany during World War II for use in heavy fighter and bomber-destroyer aircraft. Based on the 5 cm KwK 39 tank gun used in early versions of the Panzer III, the BK-5 was gas-operated and modified for aerial use, featuring an electric firing system and a 60-round magazine. The cannon fired 50x419mmR shells, with a relatively low rate of fire of around 45-50 rounds per minute. Despite its slow rate, each round was capable of devastating Allied heavy bombers, which were increasingly resistant to conventional 20mm and 30mm firepower.

The BK-5 saw limited deployment beginning in late 1943, most notably in specialized variants of the Messerschmitt Me 410 heavy fighter and experimentally in the Me 262 jet fighter. Only around 300-400 units of the BK-5 were produced. It was mounted in the nose or fuselage of select aircraft to allow for direct forward-firing capabilities, especially in bomber interception roles. While devastating when it scored hits, the weapon was criticized for its size, weight, and significant recoil, which made aiming and follow-up shots difficult. Its muzzle flash also obstructed the pilot's view, reducing accuracy during combat.

Although the BK-5 had limited battlefield success due to its handling issues and relatively late introduction, it reflected the Luftwaffe's increasing desperation to combat large formations of heavily defended Allied bombers. Its limited effectiveness, combined with the changing dynamics of air superiority, meant it was quickly overshadowed by faster-firing and more practical weapons like the MK 108 and MK 103. Nonetheless, the BK-5 remains a symbol of Germany's attempts to upscale aerial armament and represents one of the largest-caliber cannons ever fitted to a World War II fighter aircraft in operational use.