Many of you might not believe how many deer have been killed here in the Ozarks with 22lr. That up to the 22 hornet has been the poachers gun of choice for as long as I can remember. I don't like poachers.
Anyway, I am one of the ones who will tell you it is all about shot placement. Even then it will surprise you.
Case in point. I've shot several Missouri deer with .223. Always I make sure they are within 75 steps standing broadside with them picking grass, not knowing I'm even around.
One day it was real windy and cold and I decided to hunt a very heavy brush hollow. An eight point buck came in within 25 yards eating acorns. didn't know I was around. Broadside shot in the heart and the buck took off running like a scalded dog. Thought I'd missed until I seen pieces of his heart on the ground and a blood trail like 5 gallon buckets of blood poured on the ground. Tracked that deer 175 big steps before I found him.
The deer I had killed with the .223 up to that time had all either made a couple of steps and fell over dead or maybe went as much as 20 steps before dropping dead.
Deer are full of nerves. Watch them when they hear a sound. Distant sound they stop and listen. Up close sound they run. Same happens with big bullets over small. Small is like a small sting and they stop to see what happened. big slams them like a pickup truck and they automatically run.
I could go on all day typing stories of shots on deer I've taken that should've never happened according to conventional wisdom of today. Let's just say I've never hunted deer in Missouri with anything larger than 30-30 or smaller than .223, and I've not had any get away that was the fault of the gun or caliber. It was always my fault.
.243win is my choice for deer. I've seen too many taken with it not to realize it's effectiveness. But, understand that most shots taken here are under 200 yards. Out west where the closest you may get is 300.....well that may be different.