Cars do not explode.
The amount of ammunition is typically capped at a multiple of 100. The amount of ammunition should realistically be a multiple of however much is stored in each weapon's magazine.
Due to the spread of pellets, it is impossible to shoot the gun out of someone's hands with a shotgun.
It is not possible in the U.S.A. to engage in gunfights without attracting the attention of the police in minutes.