Because it has multiple barrels. This allows it to shoot faster than one barrel. At a ELI5 level they strapped 6 guns together so it shoots 6x faster than a normal machine gun.
But it’s not literally 6 whole guns. As the barrels rotate they get a bullet loaded and then rotate into a position where they get fired by a single trigger. This is faster than having one barrel because it takes a little bit of time to load and unload a barrel so by having six you can do it faster
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