If careful, a .223 is capable of safe deer harvesting. I have a really small framed female cousin that uses a .222 for deer, and has done so for the last 12-14 years now. I dont recall her ever having a "no-find", maybe because she practices all year on groundhog with same rifle, and maybe due to the ammo that her dad and I load for her.
And as somewhat mentioned above, deer have been just maimed by bigger/magnums. I have seen the same uncle mentioned above blow the leg and shoulder off a buck with a 300 Win. and it run off to never be found.
Death is not an exact science...
As they say in self-defense/CCW discussions - shot placement is everything.