While the .223 is arguably marginal for deer hunting, it is capable of getting the job done with careful shot placement.
I have used both 55 gr. NBT's and 60 grain Nosler Partition bullets to cull both whitetail does and feral hogs in south Texas. When specifically hunting deer or hogs, I used the NP's, but on more than one occasion, while predator hunting my rifle was loaded with the NBT's and they were always equal to the job, again, with careful shot placement.
I always waited for a frontal neck shot on deer and a side profile between eye and ear on hogs. The only time a 55 gr. NBT failed at the task was a full frontal shot between the eyes of a large boar. I saw that bullet impact through my scope, knocking the boar to the ground but he quickly jumped back up and disappeared back over the rise from which he came. Unfortunately, I did not recover that one and have never tried that shot again w/223. I'm convinced the bullet ricocheted off the sloped forehead, failing to penetrate the skull.
My favorite powder was H335, produced sub 1/2 moa 5 shot groups @ 3140 fps.
Regards,
hm