But of course if money is no object and you don't mind paying $100+ for 20 rounds of ammo,
Lazzeroni comes to mind,,,,,,
The 7.82 Warbird will blow most of the cartridges mentioned away, but definitely comes at a premium,
Long Magnum Cartridges
I would stick with the 300 win mag.
The boy bought a used 110 Savage 300 W/O the accutrigger from an associate at work for $200.
As was mentioned, what is your idea for "long range"?