It all goes back to what most have said on this thread. It depends on the size of the deer and where you hit them. Even here in Indiana, you could kill deer with a 22rf (NOT LEGALLY) so long as you shoot them in the ear. Even for a good shooter, if you're routinely close enough to shoot the dee you want to harvest in the ear with a 22rf, I would consider that to be less hunting and more pest control. You can claim that a 22rf has killed more deer in Texas, but you can't make that claim about Ohio, Kansas, Iowa, Illinois, Michigan, Wisconsin, or Indiana. While they are technically the same species in all states, I'd still argue that a cartridge that works very well for a white tail in South Carolina, Florida, and Texas may not be up to par in regions where a mature buck can approach 300 lbs on the hoof. Yes, you could still shoot one in the ear and kill it with a 22rf, or 223, but when a 300 lb B&C steps out into the field to check a doe at 200 yds, do you really want to trust that shot to a 55-75gr .224 cal bullet, or would you prefer a heavier bullet with enough momentum to punch through the shoulder blade and maintain a straight wound channel through the vitals? It's easy to say "the hunter should get closer", or "the hunter should wait for a better shot", but are you really willing to pass on a once in a lifetime buck because you didn't bring enough gun?
I have a 167" buck hanging on the wall that I only saw for 9 seconds. During that 9 seconds, he crossed roughly 100 yds of CRP ground. The closest he got was just over 200 yds. I shot him during a 20 min break between 2 thunderstorms, and when I took the shot, he had roughly 5 feet left before he was going to be out of my sight forever. I made a high shoulder shot on him with a 25-06 using a 115gr Nosler BT running a little over 3000 fps, and that was BARELY enough bullet and gun to break his spine. For the record, 200 yards is a gimme shot if I'm sitting in my deer stand, especially with that rifle and that load which has always shot sub 1/2 moa, and has given me groups well under 1/4 moa at that distance. He dropped, and when I got to him he was still breathing. When we butchered him, the bullet broke the spine behind the shoulder, but didn't penetrate it. That was the last time I ever hunted with that load out of that rifle. It's the most accurate load I've ever shot out of any rifle (and I have several that routinely shoot under 1/2 moa), and most would consider it to be a perfect load for whitetail. It would put meat in my freezer from now to eternity with no problem, and it didn't fail me, but I'll never hunt with it again.
So, yes a 223 will kill deer when its loaded properly, but that doesn't make it a good universal deer cartridge for everyone, everywhere.
