ACE3 has a system for linking machine gun belts where an assistant can interact with a gunner to top up the gunner's current magazine which uses setAmmo to increase the amount of ammunition in the magazine, allow the machine gun to keep firing without needing to reload.

unit setAmmo [weaponOrMuzzle, count]

If setAmmo 's count param is higher than the config count of the magazine the amount of ammunition added to the magazine is clamped to the config count

Because the magazine is only topped up to the amount it originally had there has been a lot of confusion over the years by players expecting the ammuntion now in the weapon to be the sum of the old remaining belt and the new linked belt.

If setAmmo had a an additional param to force the value of the count param then this ACE feature could function more like players expect it to.
unit setAmmo [weaponOrMuzzle, count, force]
player setAmmo [currentWeapon player, 400, true]