farmers and ranchers have used such a method for slaughtering bovines for well over 100 years. Often, the bullet doesn't pierce the foreheads of big bulls, but they still drop. then their throats are cut.

A 223 has 10x the power of a .22lr, a more pointed shape, and a hard copper jacket. The most fragile 223 sp or hp, ones that blow to frags in a sparrow, will still poke a hole in 1/4" thick mild steel plate, from 100 yds away. A friend of mine found this out the HARD way! :-) Luckily, that big old fuel tank was empty and was intended for the scrap yard!

Nature doesn't waste resources. Critters that dont butt heads, or parts of the head that don't take such impact (ie, temple) are easily pierced by 223 bullets, to 200 yds or a bit further, if near perpendicular angles of impact are achieved. The hunters ability to get close enough or shoot well enough is not the issue, really. It can be done, obviously, and the cartridge WILL do what I say. The critters drop like rocks from such hits, made with any .223 load, at ranges where the velocity still exceeds 2200 fps

The cranial vault is a "sealed-vessel", full of mostly water-tissue. High velocity impacts to such vessels fling aside those tissues with such force that skull bones crack and eyeballs pop completely out of their sockets. the brain is pulped and the animal drops instantly.

If you want to see what forces are a work, get a quart metal can, fill it with water, and center hit it with a 223 sp, softpoint, from at LEAST 10m away (for safety from flying metal frags) you will get WET if you try this from 5 yds or less distance! the can will essentially explode from the hydraulic forces unleashed by such a hit. do NOT do this with a glass container! The frags fly a long way and will always become somebody's problem, some day. As a kid, I shot right under a few frogs in the water with a 222 sp, and their bodies flew 20 ft or more, and they were dead, without a mark on them. Simple water pressure killed them instantly.