Andro Corp Industries FSB AR-15 5.56mm Threaded Rifle Barrel 10.3 inch 1-7 Twist 1/2x28 QPQ Corrosion Resistant Black B556103CSFSB. 3 FSB BARREL for your MK18 Clone build? This is your barrel Machined from 4150 CMV Steel. Melonite QPQ coating. A fast...