MK 101 cannon
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The MK 101 is the designation of a 30 mm autocannon used in German combat aircraft during World War II. Although accurate and powerful, with a high muzzle velocity, it was very heavy, with a low rate of fire, which limited its production. Wikipedia
Barrel length: 1,350 mm (53 in)
Cartridge: 30x184B, steel casing
Muzzle velocity: 900 m/s (2,953 ft/s)