Under the watchful eye of the instructor, a trainee sends rounds down range. The M2 has varying cyclic rates of fire, depending on the model. The M2HB (heavy barrel) air-cooled ground gun has a cyclical rate of 450-575 rounds per minute. The early M2 water-cooled AA guns had a cyclical rate of around 450–600 rpm. (Photo by: Patrick A. Albright/MCoE PAO Photographer) Click the photo above to see more.