With perfectly placed bullets and broadside shots even poor hunting bullet will kill them. But an "elk bullet" is one that will break heavy bone and still penetrate about 24" or more.
There are some 6.5MM bullets that will do it too, but not many of the "long range" ones will. They are made to fly well, not penetrate heavy bones and bodies.
The Creedmoor is basically a 6.5 Swede ballisticly. Use the same hunting bullets for game over 400 pounds that the Swedish do and you will be just fine. The Swede is a shell with a long history of killing moose, which are larger then elk.
Don't fall for the bait of buying bullets because "they are more accurate" for elk hunting. Elk are big! You don't need 1/3 MOA and you can't use it in the field without artificial rests anyway. 1.5 MOA is just fine for elk. They are bigger then horse flys. If your good elk bullet will shoot 1/2 MOA that great, but really not necessary.
Here are the ones I'd consider.
Norma Oryx 156 Grain Bonded Protected Point
Norma Alaskan 156 grain
Woodleigh 160 Grain Weldcore
Hornady 160 Grain RN
Nosler AccuBond Bullets 140 Grain Bonded
Nosler Partition 140 Grain
Swift A-Frame 140 Grain Bonded Semi-Spitzer
Performance inside the elk is FAR more important than performance from the gun to the elk.
Of the bullets you recommend, which ones have you killed or seen elk killed with, and what were the results?
