Quote Originally Posted by n2877 View Post
I've heard it even slows the plane down a little when fired, not sure if that is true.
Technically it is true (Newton's 2nd law) but it is not an easily measurable amount. The 30mm rounds weigh less than 1lb each, if I remember correctly, and the plane can weigh as much as 40,000lbs when loaded up. Even firing several hundred rounds over a course of a few seconds is hard to account for because of the changing dynamics of the aircraft's flight profile, angle of attack, thrust levels, drag levels, coefficient of lift, etc.