ok well i'm thinkin of startin a second ar-15 build...i was thinkin of gettin a 16" barrel...any advice on what kind to get? should i stick with a 1/8 twist? or would a 1/7 be better for a short barrel? and i'm more then likely not gonna have sights on it...gonna go with an acog or reddot scope...so does anyone know what the longest freefloating quadrail system they make is? the longest i've seen is 13.5" any advice on which brand to go with?