Or just get a BDC reticle like the Leupold Boone and Crokett and you will be good to go.
The Burris BP reticle does the same thing. Although I don't zero it the way they suggest, at 200 or 300 yards, the extra hash marks are plenty useful. In my .300WM with the 180g MRX, the second hash is 500, the third 600 - both right on the money.
