A US Marine firing a shotgun during training

A shotgun is a type of gun. To make a shotgun work, gunpowder is lit by a primer inside a shotgun shell. The gas from the burning gunpowder pushes whatever is being fired out of the barrel (usually a bullet). Originally, a shotgun shell would have small lead balls called a "buckshot" or "birdshot". Now, instead of lead shots, the cartridges have iron or steel balls, because lead in the environment can poison wildlife. The balls spread out when they are fired. Sometimes a shotgun shell will have bigger shot, of bullet size, called a "slug".