When in first person view, if you look at the minigun on the right hand side of the helicopter, when you fire, the entire weapon rotates instead of just the barrel.

This can only be seen from the first person perspective, it does not do this in third person, also this can only be seen when piloting the helicopter by yourself as the co-pilot blocks your view of the weapon otherwise. Can't determine if left side minigun does the same thing b/c the view is blocked by your shoulder.