An automatic shotgun is a form of shotgun

Shotgun

A shotgun is a firearm that is usually designed to be fired from the shoulder, which uses the energy of a fixed shell to fire a number of small spherical pellets called shot, or a solid projectile called a slug...

 that is able to fire cartridges continuously while the trigger is pressed, unlike semi-automatic weapons which require the user to depress the trigger for each projectile fired.

Design

Blowback type weapons such as this use the force of the gas (created by the accelerated deflagration of the propellant) to cycle the action, ejecting the empty shell and loading another round without any user intervention. This process is similar to all automatic weapons

Automatic firearm

An automatic firearm is a firearm that loads another round mechanically after the first round has been fired.The term can be used to refer to semi-automatic firearms, which fire one shot per single pull of the trigger , or fully automatic firearms, which will continue to load and fire ammunition...

, including machine pistol

Machine pistol

A machine pistol is a handgun-style, often magazine-fed and self-loading firearm, capable of fully automatic or burst fire, and normally chambered for pistol cartridges. The term is a literal translation of Maschinenpistole, the German term for a hand-held automatic weapon...

s and rifles

Automatic rifle

Automatic rifle is a term generally used to describe a semi-automatic rifle chambered for a rifle cartridge, capable of delivering both semi- and full automatic fire...

.

Selective fire

Selective fire

A selective fire firearm has at least one semi–automatic and one automatic mode, which is activated by means of a selector which varies depending on the weapon's design. Some selective fire weapons utilize burst fire mechanisms to limit the maximum or total number of shots fired automatically in...

  shotguns provide an optional semi-automatic

Semi-automatic shotgun

A semi-automatic shotgun is a form of shotgun that is able to fire a cartridge after every trigger squeeze, without any manual chambering of another round being required...

 mode through a switch.

Almost all automatic shotguns are fed through some sort of magazine, to provide the user with functions similar to an Assault rifle

Assault rifle

An assault rifle is a selective fire rifle that uses an intermediate cartridge and a detachable magazine. Assault rifles are the standard infantry weapons in most modern armies...

.

List of Automatic Shotguns

• Daewoo USAS-12
• Duncan Gordon CSWS belt fed 12g lmg (concept)
• Heckler & Koch HK CAWS
• AAI CAWS
• Pancor Jackhammer
  Pancor Jackhammer
  The Pancor Corporation Jackhammer is a 12-gauge, gas-operated automatic shotgun. It is one of very few fully automatic shotguns, and although patented in 1987, it never entered full-scale production. Only a few working prototypes of the Jackhammer were ever built; some sources state that only two...
  
  
• Smith & Wesson AS-3
  Smith & Wesson AS
  The S&W AS is a 12 gauge select fire shotgun manufactured by Smith & Wesson. Its layout is similar to the M16 rifle and fed from a 10 round magazine. The S&W AS was a rival to the Heckler & Koch HK CAWS....
  
  
• Auto Assault-12 Shotgun
  Atchisson Assault Shotgun
  The Auto Assault-12 , originally designed and known as the Atchisson Assault Shotgun, is a shotgun developed in 1972 by Maxwell Atchisson. The current 2005 version has been developed over 18 years since the patent was sold to Military Police Systems, Inc. The original design was the basis of...
  
   (AA-12)
• USAC (United States Army Corps) FAS-173
• Special Operations Weapon
  Special Operations Weapon
  The Special Operations Weapon was a blow-forward operated, select fire shotgun used by US Navy SEALs in the Vietnam War. It was designed by Carroll Childers, an engineer at the Naval Special Weapons Center. The 870 mod kit provided SEAL shotgunners with a quick-change magazine holding 20 rounds...
  
  
• Remington 7188