The AR-15 Platform rifle is an excellent Whitetail deer rifle provided the hunter chooses the correct ammunition for Whitetail deer.
You would not want to use a 50gr ballistic tip on a deer.
I've been using the Blackhills 60gr soft core bullets for years and the deer just drop every time.
There is a new cartridge available in the 223 manufactured by DRT Ammunition. (Do a Google Search) this bullet simply makes the deer fold.
I live in Michigan where the deer grow big. I also own 125 acres in the northern part of michigan and 20 acres in the southern part of Michigan.
I have 4 boys and we all use the AR-15 platform rifles for Whitetail deer hunting and we always get plenty of deer. As I was saying, this past year we decided to use the new DRT ammo. All 4 of my boys and myself got deer on the same day. We all talked about our hunt around the campfire that evening while sipping on hot chocolate.
Everyone of our deer shot with the new DRT did not move even one inch to the right, left, forward, or rearward: They all just folded.... (I mean simply folded)
Not one of the deer had an exit would, the energy stayed within the deer. When we cleaned them we found nothing left of the lungs but a thick jello type substance. The DRT was like a bomb going off inside the animal.
I've shot deer with 30-06's, 30-30's, 7mm mags, shotguns, and 762x39 caliber rifles and never had a deer just drop. They alway ran at least 25 yards if not 200 yards before dropping. Even with double lung hits.
This has never happened with the 223 DRT ammunition.
In my opinion nothing will drop a large Northern Whitetail deer faster than a 223 60gr DRT bullet. The second best bullet is the Blackhills 60gr bullet.