Take your pick form any caliber mentioned or you are thinking about. I have dropped deer with a 270 and with a 30-30. What you must realize is its shot placement. Hit one behind the shoulder and it will run, if you push it by looking for it too soon it will run farther. If you hit one in the shoulder most of the time you will hit the scapula and jar the spine thus producing the DRT seneria. You need to know there is no sure way to knock a deer down every time and no magical bullet or caliber that less an RPG.