This may have been brought up before, but what if instead of giving the gunner an ability beyond multiple ammo types, we add additional ammo types to make multiple ammo's more viable.
Here's a few ideas I'll throw around
Shatter rounds: Gun damage is significantly traded off for added shatter damage, for when things aren't going your way and you need a disable (great for flak, banshee and mortar to get some extra utility when the hull won't fall)
Explosive rounds: Like shatter rounds but with explosive damage, great for balloon poppers and hull strippers to get a little utility once their job is done
Reinforced rounds: Your gun takes less damage, for those merc/art assaults as you move through, sort of a reverse heatsink
A front ship specific mounted captains gun: The captain controls this gun with lmb, but it only shoots straight, anyone could load this gun, but it may be the gunner if other ammo types/load locations don't synergize well with the mounted gun
I think the shatter and explosive rounds works best, as you're likely to use that on otherwise 1 ammo type guns like gat, carro, mortar, banshee, maybe even bring merc off the charged rounds for once.
Let me know what you guys think