B17
Gun positions ejecting casing within the aircraft
1. Top turret
2. Left and right cheek guns
3. Left and right waist guns
4. Rearward observation window gun (If equipped)
Gun positions ejecting casing out of the aircraft
1. Chin turret
2. Tail turret
3. Ball turret
Any way, that would only be 3 gun positions dropping brass that could effect FPS. That assumes that brass is going to be visable from other aircraft. If it's not, adding brass casing graphics is kind of pointless, as in most planes, the pilot never sees the brass leaving his own guns.