FYI, they aren't really shooting. It's just the way other players rounds/trajectories are rendered on your your screen. You also won't see when a particular gun position in any bomber is out of bullets as long as the other player still presses "fire all".
But despite of this, if he has no bullets or no valid arc of fire, he can not and will not shoot any bullets on his client.
You just don't see it, unfortunately.