GAU-16 is the designation for the .50 BMG variant in the helicopter door-mount configuration; it has a higher rate of fire than the standard M2.
GAU-17 is the US Navy / Marine Corps designation for the M134 minigun. USAF calls it the GAU-2.
Authentic rates of fire for weapons, yes, definitely; if the engine won't support as much as we need, we will likely compensate with other means. Trajectories will be as authentic as we can get with the engine, I would hope; I'm not a coder.
