Shotgun shells are self-contained cartridges loaded with shot or slugs designed to be fired from a shotgun.
 Most shotgun shells are designed to be fired from a smoothbore shotgun barrel, however rifled shotgun barrels are gaining popularity and to that means many saboted shotgun shells have been designed for their use in rifled shotgun barrels.

 Around 1930 standards were finally set worldwide on chamber dimensions for all shotgun gauges, up to this point chamber dimensions varied greatly between countries and manufacturers so care should be taken when firing any shotgun manufactured prior to 1930.

 Many of these shotguns will have short chambers and when fired using todays more powerful ammunition extreme pressures will be exerted on the chamber area do to the fact that the shotshell crimp will actually be opening into the forcing cone area and not before it.

Shotgun, Gauges: While there has been a few gauges of shotguns since there beginning, the field of choices for gauge are now today narrowed down to:

• 10 Gauge.
• 12 Gauge.
• 16 Gauge.
• 20 Gauge.
• 28 Gauge.
• 410 Caliber, if the 410 were an actual gauge it would be 67 gauge.

Shotgun, Bore Diameters:.

• 10-Gauge = Bore Diameter of .775 inches.
• 12-Gauge = Bore Diameter of .729 inches.
• 16-Gauge = Bore Diameter of .662 inches.
• 20-Gauge = Bore Diameter of .615 inches.
• 28-Gauge = Bore Diameter of .550 inches.
• 67-Gauge = Bore Diameter of .410 inches.

Shotgun, Chamber Lengths:.

• 10-Gauge = Chamber Length of 2.875 inches - 3.500 inches.
• 12-Gauge = Chamber Length of 2.750 inches - 3.500 inches.
• 16-Gauge = Chamber Length of 2.750 inches.
• 20-Gauge = Chamber Length of 2.750 inches - 3.000 inches.
• 28-Gauge = Chamber Length of 2.875 inches.
• 67-Gauge/.410 = Chamber Length of 3.000 inches.

Shotgun, Action Types:

• Bolt-Action, Shotgun; A shotgun, that is manually loaded, cocked, and unloaded by pulling a bolt mechanism up and back to eject a spent cartridge and load another.
• Combination, Shotgun-Rifle; A shotgun with 2 or more barrels, normally a rifled rifle barrel over top of the shotgun barrel and a break open design like a single shot.
• Double-Barrel, Over and Under, Shotgun; A shotgun with two barrels, one above the other.
• Double-Barrel, Side-by-Side, Shotgun; A shotgun with two barrels, one beside the other.
• Lever Action, Shotgun; A shotgun, that is loaded, cocked, and unloaded by an external lever usually located below the receiver.
• Pump Action or Slide-Action, Shotgun; A shotgun that features a movable forearm that is manually actuated to chamber a round, eject the casing, and put another round in position to fire.
• Semi-Automatic, Shotgun; A shotgun in which each pull of the trigger results in a complete firing cycle, from discharge through reloading. It is necessary that the trigger be released and pulled for each cycle. These firearms are also called "autoloaders" or "self-loaders." The discharge and chambering of a round is either blowback operated, recoil operated, or gas operated.
• Single-Shot, Shotgun; A shotgun in which only one shell can be loaded and fired at a time.

Shotgun, Shooting Sports:

• Skeet; A clay target shooting sport with a shotgun. Shooters fire at clay targets crossing in front of them.
• Sporting Clays; Often called "golf with a shotgun," it is a sport in which shooters, using shotguns, fire at clay targets from different stations on a course laid out over varying terrain.
• Trap; A clay target shooting sport with a shotgun. Shooters fire at clay targets flying away from them. Shooters stand behind the trap at a distance from 16 to 27 yards.
• Shotgun Sports Targets; CLAY A circular, domed frangible disc used as an aerial target for shotgun shooting games. Originally formed out of clay, modern targets are a combination of pitch and limestone. Dimensions and weights are regulated by shotgun trap and skeet shooting associations. They are often called "clay pigeons".