I was hunting out of Falfurrius, Texas. I was using my AR-15 loaded with 55grain 223 JSP (like a Rem. CorLokt) over 23.0 grains of H-335. Nothing spectacular so far as the cartridge goes. It travels at about 2940 fps. It is a boar and I shot him at exactly 100 yards. I shot him in the head low and behind the ear. One shot and he was down. I really enjoyed that shot!!
Last year my 8 year old grandson shot his first deer, a doe, using the same cartridge in a NEF HandiRifle, with one shot to the heart.
I'll post some pictures of him in another thread. I am proud of that boy!
Some say a 223 is too small for deer, but if you wait for a good shot and don't rush, I think it is just fine.