Ok if I remember correct in Feild and Stream they answered this with in the past year. It was a .223 I believe and not .243 but I can't be 100%. The author actually supported it for the simple reason of low recoil for better shot placement. If you want I can find out the issue since I save them and read them again. The author actually killed them for the government I think. Hell the army uses it to kill Humans I think it can handle a deer just my .02