Positive stops are provided to maintain safe fuselage and rotor blade clearances. In addition, the fire control system will interlock firing to prevent firing signals to the gun if it is outside the firing coverage; rigging will preclude contacting the stops during operation. The XM301 gun is a three-barrel 20mm configuration, each barrel having a length of 1625.6mm (5 ft-4 inches).
Ammunition loading is provided through the swing-away nose and permits access to the feed chute. Loading can be accomplished from any partial load capacity, can occur with the rotors turning, and will not interfere with simultaneous refueling. Three soldiers will be able to refuel and rearm the Comanche under wartime conditions in 15 minutes. A rotary reel ammunition storage system with a capacity of 500 rounds is located below the aft crewman and between the keel beams. Linked ammunition is stored on the reel in a helical path.
Adjacent rows of linked ammunition on the reel are separated by a light-weight helical divider. The divider provides for constant spacing of the rounds as they are stored in the reel. The rotary reel is driven by an electric boost system responsive to gun demand. The linked ammunition is fed to the gun through a flexible chute leading from the reel to the gun. The chute permits ammunition feeding while allowing gun motion in azimuth and elevation. Automatic round counting is accomplished through the MIL-STD-1553B databus for display to the pilot and an external counter is provided for use by maintenance personnel.
The turreted gun system is driven by a 270 Vdc motor and gearbox, mounted as an integral unit to the gun. This motor accelerates the gun to the full firing rates of 750 or 1500 SPM (shots per minute) within 0.25 seconds.