Here's another idea. I noticed when trying to increase the number of planes blown up with a given ammo load, you tend to start taking shots closer in (like 100-150 yards). So perhaps using the throttle, stay 300-500 yards behind the plane and only take those shots - or maybe 4-600. Heck, for a real test, set the convergence to 650 and only take shots from 800 - 1000 yards. Those shots are a lot harder, and the number will increase because your aim is getting better and not because you're getting closer. I guess if you can make those shots, a 250 yard shot will seem tike hitting a duck in a barrel.