...hunted with 60gr to 70gr bullets at 3000+ fps
A 70 gr bullet at 3000+ fps
sounds (I'm not getting out of bed to go downstairs to peruse reloading manuals) pretty hot for a 223 Rem.
However, as many have stated, there's a difference between the .224/5.56 we shoot out of AR's and the full list of cartridges that utilize .224 caliber bullets.
A Speer .224 70gr semi-spitzer fired from an rifle chambered in 223 at 2700 fps has
less than 1000 ft/lbs of energy
at 50 yards- most would argue that's a paltry amount of oomph. At 150 yards that bullet is cruising at just 2100 fps and has less than 700 ft/lbs of energy.
That same bullet launched at 3500 fps in a 223 WSSM has 1415 ft/lbs of energy at 100yds- 40% more than the traditional cutoff for the minimum amount of bullet energy to kill a deer and at 150 yards it's flying at 2795 fps and still hits with 1215 ft/lbs of energy.
I think you're in the minority if you believe that 224 caliber bullets can't kill deer- they're used all the time and harvest plenty of deer. However, one has to search a little harder when looking for a good hunting bullet in this caliber. Most of the heavier .224 bullets on the market are match bullets and not designed for hunting (and I know there's others- I just mentioned one example). And the reason is because the 224 caliber bullet cannot reliably kill deer
consistently.
I think the debate centers around whether it's ethical to hunt with bullets in this caliber and I would agree with the OP simply because Class II animals succumb best to bullets with sectional densities over 0.2 and most of the larger 224 caliber bullets barely approach this and I only see one that has a SD of 0.214 (Swift 75 grain).
Once the bullet gets to the target, one desires the bullet to then penetrate it and damage vital organs, nerves, vessels, and anything that will minimize the animal's departure and demise. 224 caliber bullets perform marginally in this regard. One can claim success but there are undoubtedly many deer shot with 224 caliber bullets that are wounded, run off, aren't found, and suffer a prolonged death. That's not what ethical hunters want for the deer and it shouldn't be what any of us want the appearance of hunting to be by the general public- we want to bring people into shooting and hunting and if the first thought that comes into the mind of a nonhunter is that of wounding a deer with a marginally effective bullet and that animal suffering before it dies then that person not likely to ever go hunting- or possibly even shooting in general. If the thought that comes to mind is the image of hunters being primarily concerned about dispatching their prey effectively and humanely with the least amount of suffering (and subsequently filling their freezer) then that's someone who's more likely to go hunting- which is good for us all- and managed hunting is good for game too. That last point is significant as well since today's deer aren't the deer of 30+ years ago- at least not in Alabama. Today's deer are bigger and healthier.
Bullets that perform
consistently should be the minimum standard considered for the use in hunting game in any Class and for deer and other Class II animals that means bullets larger than 224 caliber.
That being said, the 224 caliber bullet is versatile and has a wide ranging role in Class I game from rabbits to squirrels, ground hogs, yotes, etc.