You can send your scope to Leupold and tell them about your bullet, velocity etc and they can put in a reticle for you. Not sure if they go past 500 though.
If you want to start shooting out past 500 I would suggest a mildot reticle with turrets. The mildots are meant as a range estimation system but they can also be used for holds. The turrets combined with accurate range estimation/range finder will be more accurate then just using the mil dots. Of course this all equals to range time and recording your data. Another thing to consider, depending on how far out you plan on shooting is how much internal adjustment your scope of choice has and perhaps the requirement of a 20MOA base.
Fella's , If you want to start shooting some long distance, 800,1000,1200 yards you better start doing some homework and forget about the scopes with dots and built in rangefinders. Get a ballistics program like sierra infinity, get yourself a GOOD tactical scope like a leupold vari-x III 6.5-20 or similar, turrets a must have.I have personally shot 7 inch groups at 1000yds with the 300 win mag using my system on a ballistics program.