How about a Hazelton booster for the appropriate aircraft.
Myth of German fire superiority From what I understand, this device boosts your rate of fire, almost doubling it in some cases, obviously the down side is you get less time pulling the trigger, so if you miss you waste twice as much ammo.
It might be considered an unfair advantage for some, but there are downsides to it's use. From what I understand it was in widespread use towards the end of the war so is not only historically correct but also, unlike the collimator gunsight, was quite common on some aircraft.
Another mod for some bombers might be the Norman gunsight.
Gunsights So Jason if the Field mods are working out, how about adding a few more ?