I have a GE demo tape that show trade show films from the late sixties and early seventies when GE was trying to market these things. about forty five minutes of sheer giggles. they show 308 cal, in long and short barrel models, 50 cal, 20 mm and 30 mm. they have two fifty cals mounted on a m113 chassis connected to a towed radar unit and that thing literally has brass pouring out of it like rain. A F100 target drone just gets sawn into little pieces. The show 20 round bursts, 100 round bursts and then they show a thousand rounds or six seconds burst on a m113 with the 20mm and when the close up shows the APC, there is a two foot hole chewed right through the near AND far walls of the track. They also showed a flip up mount that was to be used on discrete carry in a truck. the tarp of the truck covers the bed flat and a soldier pulls a lever and the minigun pops up to action in about a second. GE and Orlikon made a three barrel 57 mm AAA that made it atleast to the proto type stage, but the wieght of ammo was too much for the thing to be useful for more than one burst without resupply.
Also the CIWS or cheesewhiz vessel defense system the Navy uses on ships as a last gasp against closein targets (within the fusing range of missles) is a 20 mm selfcontained system and the Goalpost system uses the 30mm Gau 8 for land defense, during the testing of the CIWS on a barge, The weapon performed exactly as designed in ripping to shreds an incoming drone, and as the wreckage of the drone scattered, the CIWS reaimed and fired at four or five different pieces of wreckage as the parts floated down, As the parts rained on the water, a flock of gulls roosting by the barge also took off and the CIWS dutifully registered them as warheads and engaged three and turned all three into puffs of feathers before the commander of the test aborted the event.
in some movie the guy has something like this fitted to an armored up Suburban. If i recall Car and Driver magazine tested the thing,, it had a metal grate floor to lose the empties.
Ofcourse GMC will offer this next year as an option against car jackers.
http://www.ibistek.com/viper_gallery.asp?title=main