A shotgun, also called a "scattergun", is a firearm designed to shoot a multitude of lead or steel balls of varying sizes. This makes it very effective at hunting game, greatly increasing the weapon's hit potential. However, the accuracy and power found at close range diminish rapidly as you get farther away from the target. Shotguns designed for military use are often called "combat shotguns".
The riot shotgun is a semi-automatic shotgun with a drum magazine. It has high damage-per-second, due in part to its large ammunition capacity when compared to other shotguns and its high rate of fire. With the Shotgun Surgeon and And Stay Backperks, it can be a very devastating weapon in close quarters combat. It also reloads much faster than any other shotgun and therefore can change ammunition type very quickly.
There are several disadvantages with the weapon. Like most shotguns; it suffers at mid to long range due to its poor weapons spread. However, this can be countered to a certain extent by using the 12-gauge slug ammunition (which decrease spread considerably). Also, due to its rapid semi-automatic fire and fast reload, the weapon can use a large quantity of ammunition quickly, with 12 gauge shells being relatively rare, and expensive to buy in large quantities.
It is also possible to find one during a quest for the Van Graffs, at the final confrontation between the Van Graffs and Caesar's Legion where three of the Legionaries carry riot shotguns (if above level 14).