If you are going to build make sure to get your bolt and barrel from the same people and matched to each other. Ask your supplier what his headspace tolerances are. If he tells you that he headspaces within 1/1000th of minimum then you can be sure that you are dealing with a great barrel maker. Also go ahead and build it with a free floated barrel. A free floated AR with a precisely headspaced barrel made from a good blank will shoot great no matter what else goes on it... I happen to be a fan of white oak armament in this area.