Minigun

One of the most powerful weapons in GTA. The minigun is based on General Electric's M61 Vulcan Cannon (wow, this company does make everything), the mainstay gun for the US military's airplanes. It has an insane rate of fire and can annihilate most vehicles in the GTA universe in less than a second. In Vice City, the minigun was perfect for mowing down targets level with the player, however, it could not be aimed vertically manually. Instead, it shot upwards automatically, similar to the Rhino. In San Andreas, thanks to the new aiming system, the minigun could be pointed in any direction, making shooting higher targets much easier.

Locations: San Andreas

On top of the southern arc of the red bridge connecting San Fiero and Tierra Robada
Inside Mike Toreno's ranch after completing all his missions (along with the flamethrower and rocket launchers)
On the bottom-most level of and underground parking garage in northeast Las Venturas