What is the best caliber for killing a deer.
Man, that is a subject that had been debated by everybody from Elmer Kieth, Jack O'conner and everybody inbetween.
So, here we go with another opinion. First of all, I've killed over two hundred deer, and performed autopsy's on every one of them, as well as been a sponsor of youth hunts, introducing new folks into deer hunting, etc. Probaby have field dressed more than three hundred deer. Kills have been by archery, Muzzle loader, and centerfire rifle. So, I've seen the effects of a variety of calibers/bullets, and the effects they have on the internals of an animal.
I work in conjunction with the Okla Dept of Wildlife on Deer Managment Projects where areas that have an overpopulation of does need to be thinned out.
So much for all of that.
There is no Magic caliber.
There is no bullet/gun that will consistantly drop a deer in its tracks,unless it is shot in the area that will take out the central nervous system. (same for a human)
Poor bullet placement will result in a kill mostly, but some do survive a poor shot. Not many though. Often, the novice hunter will not recover the animal, as they don't have the tracking skills. I can't tell you the number of times I've got a call from a friend that shot a deer, and can't find them. They quickly give up, not knowing what to do next.
Sometimes there is a recovery, and sometimes there is coyote dinner.
I've killed deer with a 55 gr. 22-250, 55gr. .223, .303 British, .270 Win, .300 Savage, .243WSSM, 30-06, and others.(the majority of these calibers are available in AR uppers) Nothing is better than the other as far as a caliber is concerned.
What is significent is the bullet construction and how it performs when it passes through an animals cavity. The decision of what bullet to use is determined by the terrain you will be hunting.
If one is going to hunt in the west, where long shots are the norm, a bullet like the Barnes TTST that has a long sleek profile, and a high BC will work great for long shots, and give reliable expansion at long ranges.
Back east, or in eastern Okla, where shots may be limited by terrain to 100 yds or less can use a more fragile bullet that will mushroom at lower velocities.
Just my opinion, and my opinion only, the question of What is the best caliber for hunting whitetail deer in an AR upper is what ever you want to shoot.
If one has a caliber in mind, lets discuss placement, and bullets.