Back in the days when game was plentiful, a .30-30 or a .270 was probably plenty for elk.

Now however if you need to make a long shot, you need to be equipped with a flat shooting rifle that will reach out there a longer ways.

The .338 and the .300 are very similar, and they reach out a long ways for over 500 yards with a walloping punch, ideal for elk and bears.

The guide was probably troubled because with a .30-30 you might be in for a long tracking job which is a waste of his time.

The .338 and the .300 drop anything in American in its tracks. You do not need a more powerful rifle unless you go to Africa to hunt.

The .270 and the .30-06 will drop anything close in, but you need to remember that the .30-06 was designed with WW1 combat (sniping) in mind, and the .30-30 for Indians and cougars in the wild west. They wont drop a big animal at a long distance in its tracks.

It's not that easy to sneak close to big game anymore, not like it used to be.

Moose are pretty stupid and blind, and a .45-70 is probably fine for them, sure. Different subject though. You started out talking about elk.