A good behind the shoulder shot will work fine with most heavier 224 caliber bullets. I know of one savage 340 in 222 that has killed over 100 whitetails, most with 50gr SP factory ammo. It just happens to be the rife behind the truck seat and so gets used most by an older guy that I grew up hunting with. The bullet only has to penetrate 2" of rib bone/meat before it hits the void of the lungs/heart region. You just have to specifically place your shots.
I would strongly advise against head shooting deer. I have on three occasions whitnessed the aftermath of headshots gone wrong. A neighbor I used to have was famous for trying head shots all the time. The first occasion was a week after rifle season I jumped up a pretty decent 8pt that had a hanging jaw. Apparently my nieghbor shot a littel low on the head and just blew out the bottom jaw so that it hang at almost a 90% angle to the head. It wasn't pretty and the buck could hardly get up to run away, luckily I was rabbit hunting at the time and could put him out of his misery. It hadn't been deer season for 10 days so it had been at least 10 days with a hanging jaw.
The second time was when I noticed a small doe wandering aimlessly in my back field about halfway thru rifle season. It was obvious that somethign was wrong with it. I grabbed my rifle and walked back to see if it was wounded. A good protion of its head was missing from the eyes forward, both eyes were missing and part of the nose. It was still dripping so it must have happened either that day or the night before. One 100gr .243 bullet behind the shoulder ended the ordeal.
The last time was in the late extended doe only season. I heard him shooting in the morning and saw three small does run out of his woodlot and bed down in my back feild. I kind of thought that one of them might have been wounded because of the way it was running. Just to be sure I walked along the property line to see if there was any blood. Sure enough there was drips and some spray of blood. It had been a couple of hours since his shooting and he hadn't made any attempts to track so I figured it would see if it was laying dead out there and drop it off at his place. I jumped it up in the tall grass and was able to get a shot at it at the end of my field, 100gr .243 bullet thru both shoulders did the trick. The whole end of its nose was a soggy mess, looked like the bullet endered about center of the nose and exited at an angle thru the upper jaw/nose bone.
Every time I hear somebody advocating head shots on deer these times come to mind. I actually got into quite a heated arguement with my neighbor over this and we are not longer on speaking terms as a result. In his case it was ego, trying to say he was so good he could head shoot deer with his 270. If I had a dime for every time I heard "clean kill or cleam miss every time, I don't even bother to trackem, cause if they ain't laying there I missed them" The actual vital part of the deers head is very small, and moves around a lot. I'm sure it has happened to work out for a lot of guys, but its a very poor percentage shot and should never be tried for.
Don't take this as a personal insult, its not intended as such. If I had never had these negative experiences with head shot deer I would probably think it was a good place to shoot too.