308 has suffiecient Kinetic energy to kill an elk out to 400 yards. the trick is hitting the vitals at that range. A method that some subscribe to is maximum point blank range. This method takes into account the ballistics of a cartridge and the vital area of the animal you are hunting.

For example: Lets assume that an elk has a vital area approximately 12 inches square (ie 12 inches tall, and 12 inches wide). Lets further assume that you are hunting with a 308 win load with 165 gr bullets(BC .47)at a muzzle velocity of 2600 FPS. Now the maximumheight of the ballistic arch is 6 Inches above line of sight, and the minimum is 6 inches below the line of sight (12 inch vital). With this info we can calculate that the 308 win has a maximum point blank range of approx. 350 yards. The "true zero" would be 290 Yards, +5.2" at 100 yards. That puts the appex of the arc at approx 170 yards (+6 inches), and -6 inches at 345 yards. So in theory if your weapon was sighted in this way you could aim at the center of the vital area and kill an elk from muzzle to 350 yards. Now the trick becomes doping wind drift and of course getting the elk to stand still broadside to you long enough to put it all together.