A riot shotgun is a shotgun designed or modified for use as a primarily defensive weapon, primarily by the use of a short barrel. The riot shotgun is used by military personnel for guard duty and was at one time used for riot control, and is commonly used as a patrol weapon by law enforcement personnel, as well as a home defense weapon by private citizens.. Guns of this type are often labelled as tactical shotguns or special-purpose shotguns to denote the larger scope of their use; however, these are largely marketing terms.
Most riot guns are chambered in 12-gauge and can handle 2.75" "standard-length" or 3" "magnum" cartridges. Most non-shotshell loads, such as less lethal ammunition like bean bags, are made only in 12-gauge. However, 20-gauge and .410 shotguns in riot gun configuration are also available. Smaller bores are popular for home defense, as the reduced power and recoil make them more suitable for less experienced shooters who, nevertheless, may need to defend themselves in their home.
Another defining feature of riot shotguns is their high capacity. While most hunting shotguns have between 2-5 rounds capacity (often 3, to comply with regulations for bird hunting), riot shotguns generally have a magazine tube as long as the barrel, allowing for 6-9 shells to be loaded depending on the model and length of shells loaded. This provides for as many rounds as may be needed to disperse a crowd or take down multiple suspects.
Configurations of grips and stocks for riot shotguns vary widely, but virtually always feature reinforced plastic "furniture" instead of the wood common on hunting firearms. As compared to hunting shotguns, riot guns more often feature pistol grips, with or without a shoulder stock. Without a shoulder stock (or with a folding stock), a riot shotgun becomes more compact and thus able to be used in very close quarters. With the stock, the pistol grip facilitates control of the weapon and provides a more ergonomic grip when the shotgun is fired from the shoulder. Foregrips, or forends, also vary, usually with the inclusion of a pistol grip (further increasing control and absorbing recoil), and/or the addition of an accessory rail or other mounting point for a tactical light.
The multiple projectile ability of a shotgun greatly increases the probability of a hit on an assailant, and the multiple projectiles increase the likelihood of a disabling hit. Though many sizes and configurations of shotshell are used by police, among the most common is the 12-gauge 2 3/4-inch (70 mm) 00 ("double-aught") buckshot shell, which consists of 9 .33 caliber (8.5 mm) round lead balls, each of which is similar in size and velocity to a 9mm/.38 caliber handgun bullet. This shot spreads out to a greater or lesser degree depending on the barrel choke, and can be effective at ranges as far as 75 yards (70 m). The delivery of the large number of projectiles simultaneously makes the shotgun the most effective short range weapon commonly used, with a hit probability 45% greater than a submachine gun, and twice as great as an assault rifle.The ability to use shotgun slugs extends the range and penetration capability of the shotgun. Police officers in the US commonly secure a shotgun in their vehicles, for use when armed resistance is expected or at any time greater firepower than the officer's sidearm is needed.
Riot shotguns are also more limited in range than combat shotguns by the nature of their use. A combat shotgun is considered effective out to 75 yards (70 m) because on average at least 1 pellet of a 9 pellet 00 buckshot load will hit a human sized target at that range. This is enough to degrade the combat effectiveness of an enemy soldier, but it is not enough to reliably disable an assailant in a defensive situation. For that, there must be multiple hits to the target, enough that one or more pellets will hit a vital region. Generally this is well under 40 yards (37 m) with a cylinder bore barrel. Beyond this range, slugs and good iron sights are recommended, extending the range to over 100 meters.