I'd like to see a few options
Salvo: as it is now, all turrets wait until every gun is loaded
Ripple: the turret would stagger the firing of it's guns to average out the overall reload, eg. a twin would fire the #2 gun 50% into gun #1's reload, a triple 33%, quad 25%, etc.
Ranging: each turret will wait until the preceding turret's shots have landed, slowing RoF in exchange for quicker build up of hit percentage.