I like a 30 caliber bullet. I have no experience with elk. Mule deer, white tail and feral hogs only. I have used a 30/30 Win., 308 Win., 30.06 Spr and 300 Win. Mag. My No.1 choice for the past 40+ years has been the 308 Win. A 165 gr. quality hunting bullet out of a 308 Win. is a fine medium game killer. A 30.06 Spr. would be a fine choice as well .... and a I suspect a great all around choice of bullet weight would be 180 gr.

As far as taking 400-500 yard shots in the field? That's a tough shot. So many variables, not the least of which is an intimate knowledge of the arc of your rifle's load. I'd say get darned good to 300 yards and the overwhelming majority of your ethical shot opportuities will be covered.