Big Sandy Shoot, Machine Gun Paradise, United States

Most guns are described by the type of barrel used, the means of firing, the purpose of the weapon, the caliber, or the commonly accepted name for a particular variation.
Barrel types include rifled—a series of spiraled grooves or angles within the barrel—when the projectile requires an induced spin to stabilize it and smoothbore when the projectile is stabilized by other means or is undesired or unnecessary. Typically, interior barrel diameter and the associated projectile size is a means to identify gun variations. Barrel diameter is reported in several ways. The more conventional measure is reporting the interior diameter of the barrel in decimal fractions of the inch or in millimeters. Some guns—such as shotguns—report the weapon's gauge or—as in some British ordnance—the weight of the weapon's usual projectile.