This is a comlete upper in .450 Bushmaster Caliber with 20" barrel and Izzy Suppressor. Includes 4 Rd. Magazine. These uppers will mount right on your mil. spec. Lower. With a velocity of 2200 FPS, the Hornady 250 Gr. SST/FT bullet in the .450 Bushmaster "Thumper" is designed for all large North American game. Though not a long distance cartridge, accuracy has proved to be exceptional out to 200 yards with felt recoil similar to a 20 ga. shotgun. Tubular aluminum forends allow the barrel to free float from the nut forward, chrome lining in both bore and chamber makes for long barrel life and easy cleaning.