The shotgun has evolved across many levels since its inception - military, security, law enforcement, crowd/riot control, target shooting, game shooting. Generally speaking, there are three major categories concerning shotgun types - "pump-action", "break-action" and "autoloading". Pump-action types rely on manual actuation of a pumping-slide facility to fill/clear the chamber. Break-actions "break" open to expose the breech for reloading and are further divided into single-shot, dual-shot over-and-under and dual-shot side-by-side. Autoloaders, as their name implies, are designed around a self-loading action which handles loading the chamber as well as shell ejection automatically. These are sometimes mistakenly considered automatic weapons but are, by their very action, nothing more than semi-automatic firearms.
Shotgun calibers are noted through "gauges", a term used to identify the inside diameter of the barrel. The term is based on the number of lead balls (these being the same diameter as the gun's bore size) required to equal one pound. The most popular gauge is the 12-gauge which indicates twelve lead balls to equal a pound. Similarly, 28-gauge indicates twenty-eight lead balls to equal a pound. Contrary to caliber sizes used in other firearms and artillery systems, the lower the gauge value of a shotgun, the larger the bore. Thusly, a 28-gauge shotgun sports a barrel much smaller than that of a 10-gauge with the most common gauges bring 10-, 12-, 16- 20- and 28-gauge. ".410" is another gauge value though simply identified by its bore size, much smaller than the preceding 28-gauge. Smaller gauge shotguns are generally suitable for firing by smaller-framed adults and youth.
There are a total of (43) Military Combat, Security, and Related Shotguns from Origin to Present Day in the Military Factory. Entries are listed below in alphanumeric order. Flag images indicative of country of origin.