I agree with Clark. As for me, I don't shoot at 600 or even 500 yards, but seem to get a few pig shots at 400 from time to time. Take your basic 270 with a 130 grain boattail bullet at about 3000 fps and sight it in at 200 yards. Your 300, 400, and 500 yard bullet drops will be, respectively, about 7 inches, 20 inches, and 40 inches. I can shoot with country boy holdover to about 400 or a bit more and expect to hit what I'm shooting at (if the wind isn't too bad and I know the actual distance). At 500 yards, my success percentage drops considerably and I generally won't even shoot at that range. At 600 yards, I'm out of the game with the gear I have. If I really wanted to shoot at 600, I'd have to go to the next level in scope and rangefinder. That isn't cheap. I think the first scope I'd look at would be the Leupold 6.5-20X50 and be sure that it had the varmint hunter reticle. That'll cost you close to $1000. Of course, there are many other scope choices (which you will soon hear about), but they'll all be pretty expensive. As for the Nikon, I'm not fond of the circles they use for BDC. Happily, I'll bet that some folks on this forum are already successfully doing exactly what you want to do, and they'll have info on just what you need and what it'll cost.