A shotgun is a small-arms weapon, designed to be fired from the shoulder, and discharging from a smoothbore barrel a number of small shot in each charge, rather than a single projectile. Shotguns are used in the hunting of birds and small game; in some localities they are legally mandatory for the hunting of game as large as deer, as a measure of conservation, and to make the hunt more sporting. The maximum effective range of a shotgun is about 40 yards as compared with ranges ten to fifty times that figure obtainable with hunting rifles. The three principal parts of the shotgun are the barrel, the frame, and the stock. Barrels are most often mounted in pairs; the double-barreled shotgun is much more common than either the single-shot or the automatic magazine shotgun or "pump gun". Thirty inches is the usual length of the barrel. The size of the bore is expressed as a gage number, the gage being the number of spherical lead balls, having the same diameter as the bore, required to weigh one pound. In the 8-gage shotgun the bore is 0.835 inch in diameter; 10-ga., 0.775 in.; 12-ga., 0.729 in.; 16-ga., 0.662 in.; 20-ga., 0.615 in. The lightest shotgun in regular manufacture is the "four-ten", which is not sized in gage, but in caliber; its bore is 0.410 inch in diameter.
Military and law-enforcement agencies often make use of short-barreled shotguns, called "sawed-off" shotguns. The shortness of the barrel results in wider dispersion of the shot, but at the cost of materially reducing the range. Such weapons are used to arm guards at arsenals, so that a shot fired at an intruder wíll not penetrate and set off an explosive magazine; they are also used in dispersing unruly mobs, where a large number of minor casualties is more effective than a concentrated lethal blast.
