The XM133 Minigun is a 6-barrel machine-gun. The weapon is a self-powered, gas-operated variant of the M134 Minigun. It fired over 3000 rpm but was not put into production.
The XM133 is a gas-operated machine-gun. It is nearly identical to the M134 but has barrels with ports that align with the piston drive in the center of the barrel cluster.