My luckiest shot (other then a couple times I've nailed planes w/ SB, CV main guns, and from a tank w/ the 75mm) was in a different game.
In Warbirds, I was flying a JU-87-G w/ the flak gun. I was chasing a bomber back to his base and we were both really slow, but he was still pulling away from me. After 5-10 minutes of chase, he was getting close to his field, so I figured I didn't have anything to lose. I fired off a shot from what had to be > 5K away, but I couldn't tell because he was out of icon range. The shot arced up, then came down and hit him square, blowing him apart.
It was beautiful, and he was very startled.