I would say the standard 9.5 lb M70 458 would be good. Especially if you use iron sights as the factory Winchester irons are near worthless. If he is going to be using factory ammo make him use Hornady. It is the fastest 458 ammo I have seen.

No matter what bolt action he uses, as long as it is a big bore, I highly doubt he can beat a DR in timed shooting at 50yards. Good Luck.