Famine - I think he meant .50 cal (M82A1A sniper rifle and some machine guns fire this round - it isn't considered "artillery" but I can see the confusion between .50 cal and 50 cal).
It is also the round the Desert Eagle (handgun) is chambered for.
EDIT: in hindsight it doesn't really matter because 1) the rounds are most likely 7.62 NATO rounds fired from M16's. 2) If the soldiers did decide to fire, they should not have fired just 1 or 2 shots. Just like in law enforcement, if lethal force is used, it should be LETHAL. If you shoot someone, you shoot them to kill them because that is the only way to remove the threat that justifies the use of lethal force in the first place. One could argue that the soldiers didn't carry out their mission because they failed to kill everything in the car when they decided to fire on it (nevermind questions about whether or not they should have fired in the first place).