Question: why are gatling guns called miniguns?
Answer: Miniguns are called that because they're 'mini' in comparison to the gun they were based off of: gatling guns. An example of such a gatling gun would be the M61 Vulcan, chambered for 20mm Vulcan. That's one big gun. Miniguns are more often than not chambered in rifle cartridges, such as 7.62 NATO or 5.56 NATO.