M75 grenade launcher
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The M75 is a 40mm automatic grenade launcher that was used primarily as an aircraft weapon in United States service and was one of the first weapons to use the high velocity 40x53mm grenade. Wikipedia
Caliber: 40 mm
Cartridge: M384 High-Explosive, M385 Practice
Effective firing range: 2,045 yards (1,870 m)
Feed system: belt
Muzzle velocity: 790 feet per second (240 m/s)