GForce Arms 12 Gauge 20 5+1 Bullpup Semi-Auto Shotgun - Black. The GFBP is a short and handy Shotgun in the classic bullpup configuration (action and magazine behind the trigger). Bullpup shotguns accommodate a longer barrel without adding unnecessary length, and allow you to hold the weapon closer to your body. At only 3 inches longer than the Mossberg 590 Shockwave, The 29.5-inch GFBP is ideal for the narrow corridors of home defense and tactical use.