You think that's bad for modelling?
Try flying a 410 and seeing how easily the mechanics for the tail gun are knocked out, at least 60 or 70% of the time you lose both guns simultaneously to a slew of the first incoming shells. It is not fun at all.
To make things worse, the rear guns aren't even aligned vertically for 600 yards, the bullets at no time actually travel above the gunsite or are converged in any way to meet with the intended destination range making it impossible to hit out of first instinct unless you have a custom gunsite (it just reverses the forward gunsite as well for the rear position). By the time you realise you have to adjust for the target, it is usually too late, and the guns are dead.