[PeterVerney]

This is a very, very complex subject. In fact the variables are too great to have been properly computed in WWII conditions. Having done many hours of cine gun assesments, listened to lectures, and sat beside or behind pilots on practice or live firing sorties, I used to take a great deal of interest in this.
Mixed armament is a no no to start with because of the differing ballistics of the rounds
Then there is the pilot skill in flying the aircraft correctly when squeezing the tit. If the old turn and bank indicator is not correct, i.e. if there is slip or skid, then the gunsite is not correctly aligned. After that comes variation in the ammo itself, and I could be here all day.