If we're set on realism in GOIO then this is an idea that comes straight out of history. Guns jamming. Pilots in WWI had to worry about this. In part because the quality of the ammo was very poor. There was stories of pilots spending time before flying, going through their ammo and removing mishaped bullets/etc.
So how would one implement this in GOIO? Often times pilots in WWI would carry a hammer for moments when they'd have pound on the gun to dislodge a jam. Looking at GOIO, we'd have 2 possibilities I can think of:
-Gun does not go into red state but a state like with heavy fire stacks. Just requires the gunner/engineer to whack it once with a repair tool. This will of course be annoying depending on how often the gun jams. May have a low % chance or make it where the gun jams only when fired quickly or in long increments.
-Gun jams damage the weapon but the weapon still fires. Say until you whack the gun to repair it to full, each shot ticks off a small portion of gun health. This seems more reasonable and less annoying.
Now considering this, there could also be new changes for the ammo types and classes.
Say stock ammo has a higher % chance to jam. Custom ammo on the other hand does not or has it extremely low. Passive benefits to classes could change that to affect it and offset gunner's viability. To take it a step further, give limited supplies.
-Gunners gain anti weapon jam ability. As gunners are masters at their trade, they make sure ammo and weapons are well maintained. Guns will not jam when they are using them. Get unlimited custom ammo and can preload it for everyone.
-Engineers get limited ammo supplies. Engineers understand the mechanics of how guns work but don't take time to master them. Higher % chance of jamming on stock ammo, low % chance on custom.
-Pilots get even fewer supplies. % chance higher all around. These guys are bumbling idiots with guns.
When ammo supplies are used up, then being able to use custom ammo comes down to the gunner preloading. Now of course this will be heavily unpopular. Specially with noobs who like to spray clouds. But, you'd certainly be more careful with shots and gunners couldn't just sit on a gun all day doing nothing.