Gunners don't have gunner tools. They have gunner ammo.
That's the rule for now until ammo testing is determined to be finished.
I'm fairly new to GOI, but I do feel like this may be an error that is preventing gunners from becoming more than a Niche class.
The main issue is, Gunners rarely need more than two ammo types for the weapons they use. Even good gunners, the ones that use downtime to load secondary guns with specialist ammunition while buff engineers are buffing engines/prebuffing mobility parts, rarely need to use more than two ammo types in addition to normal ammo. Heatsink ammo in particular seems heavily underused despite the utility (mostly due to the penalties of using it when not about to get lit on fire.)
Gunner "tools" might not be a bad thing to look into. I do not suggest any "tools" that could be used outside of a gun, but rather active abilities along similar lines of pilot tools might be helpful for bringing a gunner in-line with the buffing engineer. Ideally these abilities would be used alongside ammo types, and would be suboptimal for a non-gunner to take.
Example Tool 1: "Active Reload"
-This tool takes the same slot as an ammo type. When selected it immediately starts a reload on your weapon. This reload is notably faster than a standard reload (33-50%), but damages the weapon through the entire duration of the reload.
-Essentially a Kerosene for a gunner, this would give an aggressive gunner the ability to make certain long-reload weapons (Hwacha) capable of firing more often and ultimately drastically increasing their overall Damage per second without touching the weapon's burst. In addition, it would allow gunners to swap ammo significantly faster at the cost of having to repair their weapon more often.
Example Tool 2: "Heatsink"
-This tool would replace heatsink clip. This active ability would immediately extinguish a weapon and render it immune to fire until the end of a reload, at a significant cost of damage output (~25% or so)
-Heatsink clip is extremely useful for a gunner, but it can be exceedingly difficult or impossible to quickly change a weapon out in time to counter a flamer (Most heatsink clips I have seen used are on weapons with fast reloads, like gatlings or mortars). When compared to chemspray, heatsink clip is without a doubt significantly weaker and used much, much less. Currently, dual-gunner ships are extremely weak to flamers due to the lack of firefighting ability gunners possess, an active ability such as this would permit gunners to continue to fire even as their engines and balloon go down in flames (which should be your engineer's job anyway!)
Example Tool 3 - "Jerry-Rig"
-When activated applies a debuff to all aspects of a weapon for the current mag (-10/15% damage, rof, range, and no turning radius), but permits the weapon to be fired, even if destroyed,until the magazine is spent.
-This "tool" would give gunners an ability that no other class has, a final "Hail Mary" salvo when facing imminent weapon destruction. As an ammunition type this tool would virtually never see use due to penalties in virtually every category, but as an active ability it could allow a gunner to clutch victory from the jaws of defeat.