A shotgun, also called a "scattergun," is a firearm designed to shoot a multitude of lead or steel balls of varying sizes, greatly increasing the weapon's hit potential. This makes it very effective at hunting game. However, the accuracy and power found at close range starts to diminish as the target gets farther away. Shotguns designed for the military's use are often called "combat shotguns."
Vastly superior to the sawed-off shotgun, the combat shotgun combines a large drum magazine with mutilating close-range damage. The only drawback is the weapon's poor reliability, as the combat shotgun deteriorates quickly. However, considering it is commonly used by human opponents, and its use in traps, you can usually find enough to keep at least one in fully working order.
Unlike the combat shotguns in previous Fallout games, the combat shotgun in Fallout 3 is not fully-automatic.
The Terrible Shotgun - Carried by the raider merchant Smiling Jack, The Terrible Shotgun deals an obscene amount of damage to targets, in exchange for a much wider spread. It's also slightly heavier.
Sim version Operation: Anchorage (add-on) - A sim-only version of the weapon which differs in health, having such a high rating as to be essentially non-degrading. It also has a cleaner, less battered appearance than the standard Fallout 3 version.