With distant origins in the west-European muskets of the seventeenth century, shotguns are unlike any other weapon category, in that they are designed to make use of the firing cone, which is otherwise considered to be a ballistics flaw and something to be eliminated. This is the effect caused when rounds are fired repeatedly on anything from handguns to assault rifles, and the recoil of the detonated gunpowder, combined with barrel flexibility, causes the bullets to be thrown off trajectory in differing angles. Shotguns, originally known as scatterguns, are designed to use this recoil effect, and attributed firing cone to a lethal advantage at close range.
Unlike ordinary cartridges, which drive a single shell head or parabellum down the bore chamber and out the barrel, shotgun rounds hold a number of small leaden pellets (popularly referred to as buckshot), which are thrown forward in a spray like effect as soon as they exit the muzzle. The propellant gunpowder is typically more potent in a shotgun, and as such gives a higher output upon triggering, to the point where visible, explosive muzzle flash can be seen.
Given their unparalled short-range power, shotguns can be effectively used both as a door breaching device and room clearing weapons, making them very popular armaments in the gangbusting precursors to SWAT teams during the 1920s prohibition era. So popular were shotguns with the police, that the weapon category saw a new renaissance following what seemed to be a final hurrah during the beginning of the twentieth century, with Benelli and Colt experimenting with pistol-grip, selective fire, and burst-mode variants, to name a few. Toned down versions sometimes appear as riot-control weapons, with rubber buckshot and low-powered cartridges used as a non lethal deterrant.
Triela uses a Winchester M1897, which was one of the first shotguns to reliably (and successfully) employ pump-action, where a spent cartridge can be ejected by slding a barrel-mounted handgrip backwards, and a new one chambered in it's place by returning the grip to it's original position. This overcomes the inconvenience of hand reloading cartridges as had been the case in earlier Winchester models, borrowing heavily from break-barrel rifle designs. So popular was the M1897 that it saw significant use by the US Army during the bitter land campaigns fought during World War I, leading to it's better known nickname as the Trench Shotgun.