Killing them is easy, killing them immediately and where you can find them not always so. The majority of "lost" elk that I have been made aware of were all shot with 6mm. As already pointed out, under ideal circumstances they can be killed with about anything. To many are lost to deer hunters whom move up to elk with deer rifles. Use all the gun you can shoot accurately and do the elk a favor. My group uses the following. 06, 300 WM, 7 mm Mag, 300 WM, 7 mm mag, 300 WBY. We kill elk every year and have yet to lose one. Oh our sample size is well over 100.