Honest question for all you guys saying he needs 33 caliber and higher cartridges, what you would recommend if he had said max of 1,000? I'm shocked at how many people are saying he "needs" that much firepower. Of course, yes, it'll work, but it's well above what is needed at only 600. If he had said 1,000, what's cartridges are above those to reach out that extra distance and still keep the velocity and energy needed?
One factor we haven't talked about is elevation. If he's shooting at 1,000' that'll require more gun than if he's shooting at 8,000ft. Bullets travel a lot farther at elevation, as we all know. At 8K, I'd have to check ballistic tables, but I'm guessing even the 30-06, 280 and 270 Win come into play for 600 yard max.