A few of the AH Members have done some exhaustive work in regards to making and providing Historical Gun Packages
Baumer, bustr, Saxman, ( AKDogg ? <--I think also )........ as well as some others
I know Baumer ( iirc ),and possibly bustr too, worked with hitech/HTC on getting the proper MIL increments to be historical accurate in game in accordance to what was used in the actual WW II war planes ( fighters, bombers, etc )
I'm sure a search of the aircraft & vehicles forum will get you some good results on this subject.....
and as Dragon Tamer posted, a lot of players just use the single center dot gunsight or even the 2 dot gun sight with one in the center and another dot slightly below center to help with firing rockets from rocket carrying capable planes... I believe it was SlapShot that first posted the single dot gunsight many many moons ago
hope this helps
TC