I’d take kill pics with a giant grain of bias as they inherently come from animals that were :
1. Hit.
2. Hit in a vital spot.
3. The bullet performed.
4. The hunter recovered the animal.
That sample is going to exclude hunters or bullets that failed in any of those.
Verification and testing. That is where the repeated success of many people repeating the same test of the same hypothesis getting the same results.
All of those people and all of those pictures are self selecting, but, many, many were admitted skeptics.
Most were reluctant adopters. Moreover, most of the early adopters and many of the current adopters don’t jump right from .300 to .223. It has been shown to be true across the scale from .284 to .243 that the bullets perform. And, shooters recognize they shoot better with less recoil in lighter rifles.
# 1 and 2, the smaller caliber inside 300 yards eliminates many misses and increase hits to vitals.
# 3, there really isn’t a question. The bullets have a giant tip and thin jackets. They will open and create carnage. Performance is on the other side thst they oldie too fast without penetration.
The myth of bullets exploding on impact without penetration has also been dispelled at .223, 6 creed velocities. Also, the myth of armored shoulders has also been dispelled. No skin, muscle, or thin scapula is going to block a bullet.
# 4 experience shows fast dying with no tracking necessary the vast majority of time. And, if the animal isn’t recovered see point #1 and 2 as a benefit to improve #4.