CQB Barrel 5.56mm 10.5 Inch Stainless Steel With Gas Tube And Pinned Gas Block. One in seven inch twist improved polygonal rifling. Stainless steel, medium contour. Extended feed ramps, bead blasted finish, carbine length gas system. 1/2x28 threads. Gas tube and pinned low profile gas block. Weighs 24 ounces. Barrel ships with gas block installed. Designed for our gas block that is one inch long (included). Standard front sight base is 1.9 inches long and will not fit. Removal and installation of the gas block dowel pin and gas block is required to complete the assembly process. Installation should be performed by a qualified gunsmith.