When things don't compute
My load, according to my chronograph with 162 A-max is 2900fps. That is fine and what it should be with my load but. With a 200 yd zero, The drop chart said to come up 7moa for 500 yards and that is low. Have to come up to 8.25 moa to hit center. To get a drop chart to works at 500, the fps has to be 2700 with a 8.25 moa. Why does it not compute right at 2900fps?