Maybe the guns (at least the automatic weapons) will use some of the same ammo as the infantry weapons? That way if you have excess ammo you can feed some into your vehicle's ammo deposit. For the shells I'd imagine you'd have to return to a base, unless you destroy someone else's vehicle and loot that, if looting vehicles is possible (I'm new, what do I know.
).
I think adding a vehicular range aspect would add new strategic value to the game, forcing players to come up with ways to hit the enemy hard and yet still remain in their vehicle team's range, otherwise you could just fly in with 5 dropships filled with itchy trigger-fingered soldiers and take out the enemy's most vital spot in one swift movement. But then again they'd have it well guarded.
I'm just talking to myself now.