I like weapons which have interesting, unique mechanics and require some skill/experience and coordination between gunner and captain to be shot efficiently.
Here's a concept for such a short-mid range weapon I've had in mind for quite a while already:
OrizaA Boomerang like weapon, which fires disks on elliptic trajectories. If the disks don't collide with an enemy/structure, they return to the weapon.
the further the gunner points the weapon to the sides or up/downwards,
the more bulged the ellipse-trajectory. At a 45° angle a perfect circle is shot, at smaller angles the ellipse is
stretched along the other axis.
Max range: roughly 1000m
Damage-Type: Impact (with projectile elimination) and/or piercing (with actual piercing behavior, allowing multiple hits).
Projectile speed: medium
Rate of fire: slow
Turret horizontal arc: 170° with a dead center of 30-60° to prevent straight shots
Turret vertical arc: 60-120° with a dead center of 10-30°. granting the weapon a similar wide arc as in the horizontal direction would cause balance issues (e.g. it'd ruin dead spot approaches on galleon-broadsides from a very high/low altitudes)
Gun tracking speed: fast.
Clipsize: 1-4
Reload speed: depending on clip size
Spread of projectiles: pin point accurate
Projectile drop: none
on a side node: this guns needs a cool, steampunkish pseudo-ballistic visor - something similar to the lumberjacks visor, just with elliptic rings which indicate how far the projectile will travel for specific angles.
I think this concept would be most interesting for a new medium weapon. Due to it's unique projectile behavior and arcs it'd probably allow a couple of interesting build types. E.g. a Oriza goldfish with a flak/mortar side with a flight style that's rather strafing like a junker than the classical "point the front end to the enemy" style. It might also allow interesting brawl galleon builds - E.g. a Oriza/Hwacha/Artemis left side would allow enemies to approach enemies with an uncommonly steep angle (while fireing Arte and Oriza).