I have been experimenting with different belts, both on fighters and SPAA, but I am not getting any different/conclusive results. What is your experience so far?
It depends on your gun. Between 20 mm to 45 mm I recommend AP or mixed belts, I’m not expecting a single fighter or interceptor to destroy a bomber currently, the focus here is damage, with armor piercing you should be able to easily disable the engines. From 50 mm to 75 mm I recommend HE belts; the american XA-38, german Me 410 B-2/U4 or even the japanese Ki-93-I Ko should be able to easily snap off wings from bombers with ease using high-explosive belts/ammunitions.