I use a calculator like this one.

http://www.biggameinfo.com/index.aspx

You will need to know your aproximate muzzle velocity, the dia of the bullet and the Ballistics Coeficient. You might be able to the find the BC on the power belt website. You could also guess until the date matches the chart you listed above. Then start changing the yardages to your likeing. You will also need your sight height from the bore of the rifle.

Let us know what kind of powder you use and about how much. If you search the internet you can usually come close to the muzzle velocity of your load. The only way to really know is to shoot it thru a chrono. And shoot it at different ranges and actually measure the drop.

The site I listed has been pretty accurate for me though.

Good luck,
Paul