Hmmmmm 'dog two calibers pop quickly into my mind for those requirements, the .240 and .257 Weatherby Magnums. Either can be "doped" into 600 yds with some practice and will take it easy on the shoulder plus double for deer duty as well. I can likewise vouch for the AWESOMENESS of the 6x24x50 PVS Swarovski, it simply makes connecting at long ranges much easier with such a tight sight picture and will show shakes that 12-16 power scopes otherwise would'nt at such ranges.

Tell him good luck,
RA

ps
For farts and giggles, why not mention to him the .257 Scramjet Lazzeroni???