Never seen this before but some thoughts.
It is a nozzle into a diffused which suggests the air is continously expanding. This could be fun way to control the weapon, as iy would behave similar to a shotgun. Up close maximum damage ring while further away reduced damage because the ring is larger.
If you do decide to add fire, I would suggest a different path. Ammo buffs effect type of damage.
Heatsink would create a cold blast that damages balloons/engines, it would because cold have a projectile arc downward while ttaveling far.
Normal rounds fly straight but dissapate quickly for hull damage.
Either greased or power rounds generate some flame, which in turn dissapates quickly and has an upward trajectory. Dashes perhaps to balloons and guns?
What also could be fun is the pushes a ship away. an effect that noth balances and provides unique opportunity to use surroundings
