Busta,
You need the ballistic coefficient of your bullet. BC's vary according to velocity, so you need a chronograph as well. When you find the magic potion for good groups, chronograph it. Shoot it at 100 and if possible, chronograph it at 100 as well. Then shoot 200. Go to a site such as biggameinfo.com and click on the ballistics calculator. Plug in your numbers for the distance you wish to have the load zeroed for and it will calculate for you. For me the 200 grain Shockwave at +3" at 100 yards puts me about 9 inches low at 225. Another necessity is a lazer rangefinder for field use.
I have not slugged the bore of my rifle. It did very well with 250 grain Shockwaves, but shines like a new penny with the 200 Shockwaves......makes me very happy!
Thanks,
bomtek44