alright I got in on this way too late for my ADHD to allow me to read the whole thread so I'll just jump in and add my .02 that may compound what has already been spoken.
223 is legal in my state. I grew up in Montana which has no caliber restrictions whatsoever. this is just a personal observation based on my local area growing up and seeing what family and acquaintances were using but a large percentage of deer were being harvested by 22lr when i was growing up. these were usually(but not always) shots to the quintessential kill zone, not shots to the head, spine or neck. I would also like to say that a point blank shot on a deer in south eastern Montana is almost unheard of. you are lucky if you can get within 100 yards of them before they bolt.
living in Idaho now the only game I'm aware of that is legal to be hunted with 22lr are grouse with everything else either being shotgun only(turkey) or centerfire(everything else) so 204 ruger or 223 is the smallest many people go. I always hunted with 243, my best friend usually hunted 30-30 and my older brother usually either packed his 243(until it became a christmas present for my little brother) or his 7mm REM MAG(total overkill IMHO) but while I was on active duty I commissioned my brother to build me an Tahunua001-SPEC AR15 in 5.56/223 and he whined the entire time he built it that it was going to weigh 10 pounds and be unbalanced as heck and only good as a benchrest rifle until I recieved an email one day titled "I hate you sometimes".
interested in what this was all about I opened it and it contained 2 photos. the first was my older brother standing over a 200 pound whitetail buck holding MY AR15 that he had just recently finished building. the second was a google earth screen shot marking out where the shot took place, 250 yards. I guess he decided my specs were not nearly as bad as he originally suspected.
223 is more than just a varmint round and is more than powerful enough for deer, though limited personal experience with pronghorn shows that you may need more energy at long range than what a 223 is capable of delivering. I was never able to get within 600 yards of those skittish beasts and I would barely trust a 223 to take down a skunk at that range.
all guns lost in a tragic smelting accident.
I never said half the crap people said I did-Albert Einstein
You can't believe everything you read on the internet-Benjamin Franklin
Bean counters told me I couldn't fire a man for being in a wheelchair, did it anyway. Ramps are expensive.-Cave Johnson.