I have no doubt a .243 will kill a deer but I wouldn't consider it even marginal for elk.I loaded 90 accubonds in my son's .243 in front of 42.5 gr of H4350.We killed 4 deer with that load last year and only got a complete passthrough one time.The deer all died but there's a huge difference between a 100lb whitetail and a 800lb elk with heavy bones.