Shotgun Definition:
 Our modern definition of a shotgun is: A shoulder firearm with a smooth bore, designed to fire small pellets, shot, or rifled slugs, a gun with no grooves in its barrel.

 Shotgun Standards:
 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.

 Since 1926 SAAMI (Sporting Arms and Ammunition Manufacturers Institute) has been the principle organization in the United States actively engaged in the development and promulgation of product standards for firearms and ammunition.

 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 10ga., 12ga., 16ga., 20ga., 28ga. and .410cal. if the 410 were an actual gauge it would be 67 gauge.

 Shotgun Bore Diameter:
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 Length:
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 Power and Range:
 Many people wonder just how far away that a shotgun will kill, this is determined primarily by the size or weight of the pellet being fired, lead shot will retain energy better at longer ranges. Gauge, choke or oz. of shot only increase your chances of a hit.

 Shotgun Action Types:
 Bolt-action shotguns; 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; A shotgun with two barrels, one above the other.
 Double-barrel, side-by-side; 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 or slide-action shotguns; 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 shotguns; 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 shotguns; A shotgun in which only one shell can be loaded and fired at a time.

 Shotgun 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 Shooting; 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".