You might want to try AH in the offline mode--in offline mode, there will be "drone" P-51's named after HTC staffers orbiting your airfield. These drones will re-appear after you kill them.
Take off and practice shooting at these drones from different angles (tail, diving attacks, side attacks, head-on, etc)--watch your tracers, where you hit, where you miss, etc. Eventually you will get a good feel for gunnery.
The F6F is a great plane to learn shooting in. The .50's have good firing properties, you have a great ammo load and the F6F has pretty decent view over the nose for pulling lead.
Generally, the more the enemy plane is maneuvering, the more lead you will require and the closer you will want to open fire. Shooting an unmaneuvering target is pretty easy at 500 yards; hitting a wildly evading target at 500 is almost impossible and can even be tough at 250.
375 is a good distance for convergence. Feel free to experiment with it--find a setting you like. Try to set your convergence at a distance where you find yourself shooting at when you're online. When I fly a plane with 6 x .50's, I set mine to 375-325-275, to give a "spread" of fire over a range of distances.
Finally, if you haven't already, use the PAGEUP key to move your foreward view up a little (but not so much that it makes your gunsight disappear). Then use F10 to save this new foreward view--this will give you even better views over the nose for deflection shooting. If you mess up the view, don't worry--the HOME key (next to pageup) will move the view back to default.
If you become confident with your shooting abilities, try shooting with tracers turned OFF. Some pilots like that setting because, if you're a good shot, tracers will serve no purpose except to tell the enemy when you're shooting at him. For now though, leave the tracers ON because they'll be a helpful tool for you.
In short, practice, practice, practice.
J_A_B
