I set all my US .50s to d600 for all the planes that have them. They have good ballistics and can easily reach out there. This gives me a good distance shot, and a nice spread pattern to chew through multiple sections of a plane at closer ranges. I would get more punch close in if I didn't do this, but it does make it easier to land hits. I set my guns on my P38 to the same, if nothing else to keep my vertical aim point constant. Still, with the guns packed together it will rip a gorge out of targeted aircraft.
I use the .50s for pecking, harrassing and splattering, and I use the cannon mostly only when I get close in with a good shot. Saves the ammo and gives you that added punch up and personal like. I still set the cannon to d600 as well to make sure that this verticle alignment is the same as the machineguns (which if I'm firing the cannon are already blazing happily). At closer ranges there really is no spread anyway, so the pattern for the .50s is tight and the cannon will not differ much till you get out past at least d400. The US cannons do fly well though (or are those british hispano or whatever?). I wouldnt be afraid to take a cannon shot out to d600 at something large and or slow&low.
All that being said, I should still probably experiment with the convergence in non nose armed ships and pull it in a little. 68Slayer gets a hell of a lot of kills, and I would highly reccomend taking his settings under close advisement. Settle on whatever is most comfortable to you, or most apropriate for your mission.
