Know the origins...
The Minigun is a 7.62 mm, multi-barrel machine gun with a high rate of fire (up to 6,000 rounds per minute), employing Gatling-style rotating barrels with an external power source. In popular culture, the term "minigun" has come to refer to any externally-powered Gatling gun of rifle caliber, though the term is sometimes used to refer to guns of similar rates of fire and configuration, regardless of power source and caliber. Specifically, minigun refers to a single weapon, originally produced by General Electric. The "mini" of the name is in comparison to designs that use a similar firing mechanism but larger shells, such as General Electric's earlier 20 mm M61 Vulcan.
The ancestor to the modern minigun was made in the 1860s. Richard Jordan Gatling replaced the hand cranked mechanism of a rifle-caliber Gatling gun with an electric motor, a relatively new invention at the time. Even after Gatling slowed down the mechanism, the new electric-powered Gatling gun had a theoretical rate of fire of 3,000 rounds per minute, roughly three times the rate of a typical modern, single-barreled machine gun.
In order to develop a weapon with a more reliable, higher rate of fire, General Electric designers scaled down the rotating-barrel 20 mm M61 Vulcan cannon for 7.62 x 51 mm NATO ammunition. The resulting weapon, designated XM134 and known popularly as the Minigun, could fire up to 4,000 rounds per minute without overheating.
Airsoft gun version comes in the early 90s. The first manufactured by the Toy-Tec company. It was a gas-electric hybrid. The engine was powered by battery, and gas fired BBs.