Look and shoot, which is how it actually functions with Apache's head mounted display and Target Acquisition Designation Sight (TADS). I tested this functionality with the Oculus Rift DK2 and it works great.
The only problem is that the gun muzzle points directly to the point on the ground you are looking at, so I'll need to develop a ballistic computer to calculate bullet drop and airspeed shift. I already have some of the equations necessary to make these calculations, which will need to adjust the pitch and yaw of the muzzle depending on the following variables; ballistic drop, line of sight slant range to target, pitch and yaw angle to target (local ref), and the longitudinal, lateral and vertical speed of the aircraft. At the moment, if you have a high forward airspeed, the rounds impact ahead of the target, in the direction of flight, and below the target in the direction of bullet drop, and obviously the greater the distance, the more exaggerated this becomes.
Regards,
Uriah