Characteristics
The primary characteristic of a riot shotgun is a "short" barrel (generally 14 to 20" long; 18" is the shortest length available in the U.S. that is not subject to additional federal BATFE regulation) which makes the shotgun more compact and easier to handle, easier to stow inside a police vehicle, and more suitable for quick aiming at (close) stationary targets. Generally they have an open (cylinder-bore) choke, to permit the shot to spread quickly and to allow use with other types of projectiles, and they may be equipped with bead, rifle, or ghost-ring sights. Riot guns are most often pump-action due to this design's lower cost and higher reliability, although in recent years a number of semi-automatic shotguns designed primarily for defensive use have become available and are used by military, law enforcement and civilians alike.
Most riot guns are chambered in 12-gauge and can handle either 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 available. Smaller bores are popular for home defense, as the reduced power and recoil make them more suitable for less experienced shooters who are recoil-sensitive.
While most hunting shotguns hold between 2 to 5 shells (often 3 shells, to comply with U.S. regulations for migratory bird hunting), riot shotguns can have a magazine tube as long as the barrel, allowing for 6 to 10 shells to be loaded depending on the model, barrel length, and type of shells loaded.
Configurations of grips and stocks for riot shotguns vary widely, but often feature reinforced plastic "furniture" instead of the wood common on hunting firearms. Wood was used for riot gun stocks in the past, and sometimes still is. 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 is able to be brought to bear more rapidly 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, often with the inclusion of a pistol-grip fore-end (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 23⁄4-inch (70 mm) 00 ("double-ought") buckshot shell, which consists of 8 or 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 (which actually have a diameter of .354-.357"). 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). Also popular is the #4 buckshot load, which sacrifices individual pellet size (each pellet is about .24 caliber) for greater numbers (usually 21 pellets per shell) and is very effective at most indoor ranges (<50 feet), where the shot has less distance in which to scatter and thus hits the target in a relatively localized pattern. "Deer slugs" (1 oz rifled slugs) provide a powerful, accurate shot with minimal spread, but more risk of overpenetration. "Hybrid" loads combining different sizes of shot, or a slug and shot, are available but less common. These cartridges generally advertise a compromise or "best of both worlds" between the power of slugs or buckshot and the spread of smaller pellets.
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.
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