I wanna build an AR.... My goal is to make a sort of a sniper assault rifle.... I wanna do semi long range shooting... I know people have chambered their rifles to fire the 5.45. 5.56 or even the 7.62.... which one do you guys think would be the best for the task? which one would shoot farther and have power??? Since I am new to building and to guns in general I would appreciate any opinions you guys can share with me.