Unless his interests change, he will probably be the guy who goes out and buys a box or two of factory ammo, checks zero and goes hunting.
This is critical information. If you decide not to ask him, then get something that's easy to feed off of the shelf in a big-box store. I'd say 30-06, but I chronographed a ton of 30-06 ammo in the few years before the pandemic and it's a lot closer to the 308 than the ammo makers would have you believe.
That said, 308, 30-06, and 270 would be my choices. There are still a few Remington 700 Package rifles available in those calibers and they're quite the bargain. Just replace the scope and mounts and you're good to go.
Okie John
Okie John is spot on.
Most 30-06 ammo is downloaded due to all the very old rifles chambered for the 30-06 floating around out there. Yes, some of them are actually over 100 years old. So the cartridge companies do not load the 30-06 anywhere near to its potential. A modern action such as a Tikka T3 can take a substantially wamer handload that you simply are not going to find in off the shelf ammo.
I have shot .308 handloads and 30-06 factory ammo and had the .308s actually clock faster velocities. Not a fair comparison, but something to consider if you are going to be using factory ammo. If I was only looking to use factory ammo, I would opt for the .308.
A T3 in .308 would be a top choice. Besides there are tons of factory loads (normally) available, and you can handload for virtually anything on the continent. The .308 is a well proven elk killer. It is very easy to shoot well, and I have yet to see a T3 in .308 that did not drive tacks.
