The IWI TS12 is a semi-automatic 12-ga. shotgun with a 3" chamber that operates via a short-stroke gas piston. The piston has two settings that control the amount of gas that is siphoned off each ...

Barrel: Shotguns have one, two, or very occasionally, three barrels. Each shotgun gauge has its nominal diameter. For instance, a 12-gauge’s nominal bore is .729 inches.