Im just thinking of a what-if scenario for heavy clip.
What if instead of reduced ammo clip, it gave reduced fire rate? I'm not sure how much (if at all) that would change hwacha and gatling applications, but it would surely affect the heavy carronade, since currently the ammo decrease doesn't.
You get the benefit of no spread, but to achieve it you sacrifice dps across the clip. How much sacrifice is of course up to debate.