I don't know what scope you have now but it's possible you can get BDC knobs for it. I added BDC knobs on my Leupold 6.5x20x40for my 7mmRUM. They have adjustment out to 1000 yards but I've only practiced with them out to 500 yards. Below is a link to the place I bought them from. Funny thing is I spent the money on the scope upgrades and time reloading and practicing out to 500 yards and ended up shooting my Mulie at 300 yards. Below you can see the BDCknob on my scope.

http://www.kentonindustries.com/