It's not the guns. It's the bombers' full-out-non-stop FFT speed. Historically they rarely ever reached these speeds. In AH they only ever reach anything lower when they're taking off (and not even landing, most don't bother with that part of the game).
They *wouldn't* get 1.2k shots off on you if you weren't struggling to keep up with them in a fighter (bombers outrunning fighters, right. Like THAT was the norm!). They would be flying slower, you would be flying faster, you wouldn't loiter behind them, you'd be able to actually overtake them, set up slashing runs, side runs, attacks from anywhere other than dead 6, where the speeds involved mean that they can shoot further (you're heading into the bullets from dead 6). Once I'm ahead or abeam of a bomber, the most they can ever hope to ping me is at 800, 600 or less more realistically. It's only the aft angle that allows such long range shots.
And it's all because of the retarded speed of bombers. A second fuel burn for heavy bombers would solve this problem. Just bump it up 4x (so instead of 25% for 1+ hours flight time, you need 100% for 1+ hours flight time).