I'm actually a little curious how screwy bullets fly when they're shot perpendicular to a high speed. Door gunners on a chopper are the closest I can think of, but I'm not sure how accurate they are in general and I don't know how less a 7.62 round would lose course vs a 9mm.

Edit: The guns on an AC-130 or any comparable craft would probably be moving faster, but from my vast military knowledge of Call of Duty, I know that the rounds they fire are even larger.