did you violate the back? Whats your reasoning for sinew backing and osage this long? The bows that I sinew used typically 2-3 oz, but they are 50-54" long. Im guessing it would be the same for a bow that long because it would more dispursed, and a thick backing isn't necessary, but sinewing a bow that long will just add weight. If you are trying to save a violated back, a lighter backing of a different material would probably be better, like a thin rawhide.