A shotgun is a generally a smoothbore firearm, which means that the inside of the barrel is not rifled. Preceding smoothbore firearms such as the musket, were widely used by armies in the 18th century. The direct ancestor to the shotgun, the blunderbuss, was also used in a similar variety of roles from self defence to riot control. It was often used by cavalry troops due to its generally shorter length and ease of use. However, in the 19th century, these weapons were largely replaced on the battlefield with breechloading rifled firearms, which were more accurate over longer ranges. The military value of shotguns was rediscovered in the First World War, when American forces used 12-gauge pump action shotguns in close-quarters trench fighting to great effect. Since then, it has been used in a variety of roles in civilian, law enforcement, and military applications.

The shot pellets from a shotgun spread upon leaving the barrel, and the power of the burning charge is divided among the pellets, which means that the energy of any one ball of shot is fairly low. In a hunting context, this makes shotguns useful primarily for hunting birds and other small game. However, in a military or law enforcement context, the large number of projectiles makes the shotgun useful as a close quarters combat weapon or a defensive weapon. Shotguns are also used for target shooting sports such as skeet, trap, and sporting clays. These involve shooting clay disks, known as clay pigeons, thrown in various ways.

Characteristics

Shotguns come in a wide variety of forms, from very small up to massive punt guns, and in nearly every type of firearm operating mechanism. The common characteristics that make a shotgun unique center around the requirements of firing shot. These features are the features typical of a shotgun shell, namely a relatively short, wide cartridge, with straight walls, and operating at a relatively low pressure.

Ammunition for shotguns is referred to in the USA as shotgun shells, shotshells, or just shells (when it is not likely to be confused with artillery shells). The term cartridges is standard usage in the United Kingdom.

The shot is usually fired from a smoothbore barrel; another configuration is the rifled slug barrel, which fires more accurate solitary projectiles (though some slugs can also be fired from smoothbore weapons).

Uses

Aside from the most common use against small, fast moving targets, the shotgun has several advantages when used against still targets. First, it has enormous stopping power at short range, more than nearly all handguns and many rifles. The wide spread of shot produced by the gun makes it easier to aim and to be used by inexperienced marksmen. A typical self-defense load of buckshot contains 8-27 large lead pellets, resulting in many wound tracks in the target. Also, unlike a rifle bullet, each pellet of shot is less likely to penetrate walls and hit bystanders. It is favored by law enforcement for its low penetration and high stopping power.