@BillW,
(continued from above)
How high or low one places the "bead" in the "v" takes care of the rising of the bullet over the first two hundred yards or the lowering of the bullet there after. We only did this at basic training when we used M-14 rifles - highly accurate weapons. In AIT we used M-16's and training for jungle.warfare (for the most part, action would be right in front of you are distances of less than 30-40 yards). M-16's were also noted for their inaccuracy at much longer distances.
One cheat they taught us was, when in doubt aim low. The targets were mounted on mounds and if you skipped a bullet in there, it would bounce up and hit the target.