"The ammunition is separate loading. Two rounds are carried on the vehicle and the rest in the supporting vehicle. The normal rate of fire is one round every two minutes but two rounds a minute can be fired for short periods.
Fire-control equipment consists of a panoramic sight M115 (magnification of ×4 and 10° field of view) for indirect fire, telescope M116C (magnification of ×3 and 13° field of view) for direct fire, elevation quadrant M15 and gunner's quadrant M1A1."
Source: http://www.army-guide.com/eng/product1778.html