.338 is probably the prefered Elk cal...
Personally I've witnessed a 800lb Elk go down with a 7mm-08 topped off with a Hornaday Interbond bullet..
And it was One shot kill........
I also elk hunt with a person that uses only a 6.5 x .284 loaded with a Barns TSX..
I use a 30-06 and it does the job just fine...
Several others use the .270 and 7mm Rem mag, and .300 win mag...
The bottem line is, choose the biggest cal you can handle accuratley and top it off with a premium bullet and place your shot in the vitals....