New "Cold War Era Surplus" 20mm Dummy Round OEM DISPLAY PAPERWEIGHT Fired by the 20mm M61 Vulcan Gatling Gun The M61 Vulcan is a hydraulically, electrically, or pneumatically driven, six-barrel, air-cooled, electrically fired Gatling-style rotary cannon which fires 20 mm × 102 mm (0.787 in × 4.016 in) rounds at an extremely high rate (typically 6,000 rounds per minute). The M61 and its derivatives have been the principal cannon armament of United States military fixed-wing aircraft for over sixty years.[2]