Kweassa,
I suspect you do not fly bombers very often. The guns are far from accurate, and since there is no magical way for them to know how far away the target is you're firing at, the convergence is way off. You can hit a plane with maybe one gun at a time until they fly through the sweet spot, but since that sweet spot is as about 200 yards, the guns on a bomber are pretty useless for fighting off all but the most incompetent (eg, slowly approaching from the 6) attacks.