I always have my heavy carronade gunner bring heavy clip and lochnager ammo. Heavy for the initial shots to test maximum range, lochnager thereafter, and back to heavy whenever in combat (can't risk the gun being damaged and blowing itself up).
I also like heavy clip in the light carronade compared to greased if an engineer is likely to occasionally mount it (like on the side of a Goldfish).
Obviously the Minotaur benefits greatly from heavy clip.
Sometimes I'll have a gatling gunner bring heavy clip in certain positions... namely, bottom of a Junker that has an Artemis and a gatling (burst, heavy, greased [I gave up on lesmok for the gatling to prevent myself from using my close-range side at longer ranges]), or a Pyramidion gatling (lesmok, heavy, and greased). Heavy clip is lovely for targeting specific components but also great for hitting an enemy Junker's main deck accurately.
If I run a hwacha with a gunner (as opposed to a mallet-spanner-buffing engineer with burst), heavy is always the first clip when outside of combat. I personally wish it were a bit more necessary because, as we all know, hwacha is overpowered at medium-long range with burst.
I never bother with heavy in the banshee or flare gun..., but I understand the reasons people do... I just don't agree
I think heavy clip is great, but I wish the clip reduction was just a little less restrictive... instead of a 25% reduction, 20% would be sooo much nicer for that gatling gun