As previously noted, proper shot placement is the key. Many cartridges are adequate for Elk, from .270Win. on up. When I lived in Wyoming two of the most popular seemed
to be the 7mm Rem. Magnum, and the 30-06. The .338 Win Mag. was a good Elk cartridge too. But, for a "hammer", I'd recommend the .375 H&H Mag.
- still requires good shot placement though.