Centurion bp 12. The Century Arms Centurion BP-12 Shotgun delivers superior performance. In addition it is consistent in a reliable and durable semi-automatic Bullpup shotgun platform. The BP-12 is chambered in 12 gauge with a 3-inch chamber and 20-inch barrel. It features flip-up sights, a rubber recoil pad, and a 5 round magazine. This model also includes two interchangeable pistons. This allows you effectively shoot 2-3/4″ and 3″ shells interchangeably. Also with any ammunition of the proper gauge for your firearm with flawless performance.