Wow sounds like a well thought out blueprint and an amazing opportunity!
If I were building something like that I'd skip over any of the ping pong balls. Even if he is setting such reasonable limits upon himself as 450-500 it still makes sense to keep drift at an absolute minimum.
175 LRAB if he is against "using target bullets for game" as some are; otherwise a 162 gr AMax, 180 VLD or Hunting Hybrid would be my first choices. As has been pointed out, that thing ought to shoot anything and everything really well so the choice ought to be his.
I hope we can see results of the build and ESPECIALLY the hunt!
