Would that then push the idea of circle-based targetting? If full-auto generates a lot of shots, if you have it cone-based then that means a lot of stray shots that will whistle by the target and hit anything else in the way. A circle-based system would ensure that the shots go in roughly the right area, adding a measure of control to where the burst of shots go.
EDIT: I just rapidly prototyped fully automatic by fiddling the weapons_gc.xml file. The only way that I can describe a machinegun firing 25 shots off all at once is WAAAAAGH DAKKADAKKADAKKA.