Shotguns are firearms typically fired from the shoulder that are designed to fire shotshells containing anywhere from one large projectile to as many as several hundred small pellets. Shotguns aren't classified by caliber but come in different gauges . The gauge of a shotgun is determined by the number of round lead balls of bore diameter that it takes to equal one pound. Although some newer shotgun barrels are produced with rifling, shotguns have traditionally had smooth bored barrels. Except in some rare cases the projectiles fired from them cannot be matched back to the shotgun.
Shotguns come in a number of different styles and actions.
Shotguns are typically manufactured with what is called a choke in their barrels. A choke is a constriction in the last couple of inches in the barrel and can vary in the degree of constriction. A barrel that has no choke is referred to as a cylinder-bore barrel. Extreme constriction or choke can be seen at the muzzle. Shotguns can be manufactured with a permanent fixed choke or can have the muzzle of the barrel machined in a way to accept interchangeable or adjustable choke tubes.