There is the option when in a firing position to fire all available guns which can be brought to bear. A good example of this is jump into a PT boat position and point in a general direction and hit the "N" key. By default, the "N" key on the keyboard is set up as "Fire all guns". In a PT boat, if you are firing to the front position, all guns exept the 40MM will fire, as the 40 MM cannot fire forwards.
In the below quick example, I am in the tail guns firing using the "N" key straight to the rear and level. Notice the turrent, tail, and belly are all firing together. The side guns are unable to fire directly behind the plane, therefor they are not firing.

Distance wise I am unsure of the convergence, but 600 sounds good. Normally I can aim a little high at 1K and score enough hits to cripple or kill a con.
