Actually, I quite like this idea--even if it more ascetic then tactical. What if we examined the percentage of turn that it takes to fire the chaingun? Say, 5 founds take the entire turn, it is a waste if your enemy dies in 2 shots (especially if you have multiple targets).
So, how about this: a controlled burst of between 2-3 shots that take only 50-75% of a turn and long bursts that fire 5-6 shots but take up 100% of a turn. Further, these full-bursts could be used sequentially (say getting an extra-maximum of one or two shots per turn), but with penalty to accuracy when the target is changed (after all, if you have the trigger glued down and you change targets, the bullets have to go somewhere--and could hit multiple targets).