Part arrived in a timely manner. Description on arrival: -11.5" bbl, heavy, with M4 extension, and hole drilled in correct place Top-Dead-Center, and offset from barrel shoulder the correct distance. Marking on the barrel "1:9 5.56 NATO". M4 cuts in extension were well cut and as good as BCM or Model1. Initial thoughts: -Barrel is heavy, but for the price it won't lack in performance. If you want lighter, pay 2-3x as much for a BCM. Assembly: -I assembled my upper last night and the barrel assembled easily with an after-market 0.75" gas block and free-float handguard. Everything went together easily with a snug fit. The carrier mated with barrel well, so M4 extension was in the right orientation to barrel. A2 flash hider assembled to barrel with crush washer without incident. Operation: -I have yet to shoot the upper on an AR pistol, but will try to update my review after to tell of barrel performance. I have no doubts that it will perform as well as it assembled. Buyer Beware: *NFA item* As this is a barrel less than 16", to assemble an upper and attach it to a rifle is a felony, as you will have created a short barrelled rifle (SBR) without a tax stamp, and if caught, that is a one way ticket to never getting to own a gun for the rest of your life. If you attach it to an AR pistol lower or legal machine gun or licensed short barrelled rifle there is no felony. But then again, I'm not a lawyer, just a law-abiding citizen, in any case, consult your friendly neighbor BATF agent prior to assembling any parts, but again, buyer beware. I would buy this product again.