RE: 223 cal for Deer
I guess you could kill a deer with a sling shot if you hit it just right ... but does that make it right? I would never use a .22cal for deer ... if you can handle the recoil of a .22cal centerfire, you could just as easily handle a .243 (which is marginal to me anyway). Far better would be the light kicking .30-30 or something similar.