Luth-AR Lightweight Complete Upper Barrel Receiver Assembly 5.56mm 20in 11.5in HBAR Carbine 1x9 1/2x28 Picatinny Key MOD A2 Flash Hider Anodized. 56mm Lightweight barrel made from 4150 Chrome Molly with a 1-9 twist mated to Luth-AR A3 Flattop receiver...