This photo is of a UH-1C "Falcon" gunship from the 155th AHC on a gun run with his miniguns firing. Although there were two miniguns on the aircraft (one on each side outboard of the rocket pods), in the Sharks we often only fired one minigun at a time. It saved ammo, and you kinda get the idea that one gun at a time was probably enough. Keep in mind that there was a 4-to-1 tracer-to-ball ammo mix, so there were four bullets you can't see in between each tracer round you can see. Our "normal" rate of fire was the slower 3,000 rounds per minute, although the gun's maximum rate was 4,000 rounds per minute. Doing the math, 3,000 rounds per minute works out to FIFTY rounds per SECOND! -- and that's at the SLOW rate, and only from ONE gun. Each "Charlie-Model" Huey gunship carried about 10,000 rounds of 7.62mm machine gun rounds, 4,000 per minigun (one each side) and 1,000 rounds per door gunner (one each side). The low, horizontal flashing light that appears to be coming from the stream of tracers is probably the rotating beacon of another low-flying helicopter, perhaps this helicopter's gunship lead.
(Photo property of Mark Stuart)