Caliber: .223 - Barrel: 14.5 - Receiver: A4 Flat-Top Forged - The 5.56 Midlength Tactical Evo 14.5 Upper is a short barreled upper that incorporates the patented Adams Arms technology and the Samson Evolution free floating forearm. The midlength piston system will give you the benefits of a longer forearm by giving the user a longer more ergonomic grip a longer sight radius between the front and the rear sight for quicker sight acquisition and less felt recoil. The piston system parts and the barrel have been treated with our salt nitride Meloniting process making them harder and more corrosive resistant than hard chrome. The free floating forearm was manufactured for us by Samson Manufacturing and is a 12.37 tube that extends around the gas block giving you enough space to mount the removeable picatinny rail pieces to meet any of your needs.