I've probably taken over 100 deer with a 223, yes they kill deer, yes they will kill a deer at 500yards if you hit them right, but you won't find but a fraction of them.
I've killed a lot of deer way beyond 500, many past 750, more than a couple past a grand, so this is what I have found from shooting deer with a 223 and at extended range with other rifles.
1) the first blood you will normaly find will be after you see the dead deer shot with a 223
2) they will all run with a 223 unless you take out the CNS (brain/spine)
3) at 500 yards your deer runs out of sight it is extremely diffacult to find where the deer was standing at the shot without snow cover and still hard with it
4) the more distance increases the more it exacerbates #3
5) there are no bullets suitable for deer made in .224 that have a high SD and BC which is what you need for long range accuracy
if you shoot 1/4 moa from a bench at 100 yards, and at 500 yards your shooting 1MOA, most likely the bullet is a lower BC/SD bullet which just doesn't fly well as range increases, I have proved this many times with many rifles.
take a fast twist 223 loaded with a 75 gr a-max and its fun to shoot targets at 750, but the 223 will never be a 500 yard deer rifle with todays technology, nor in the foreseable future.
Its just the way it is
RR