I have noticed on my bullets that it doesn not take much for the tip to get damaged. One side of the hole can get dinged and then whatever it hits can force it closed. A bigger hole will take more damage/deformation before failure.
I was watching a few videos on terminal ballistic performance last night, and every maker has a different story of why their bullets are better and how they do more damage. Hammer says their pedals come off to make a square front, but a mushroomed bullet usually has a pretty wide/flat front anyway. If a square front was all that great, I'd shoot square front bullets to begin with and to hell with the bc.
Shooting critters way out there is fine, but the bullet has to be reliable, and the game willing to die. I shot a rabbit in the head (brain) several times and it just stood there dripping blood and looking at me. I ended up shooting it 5 times and it still took a long time to die. And that's just a rabbit! They are usually bang-flops. I was right on top of this one too.
I shot a doe several years ago with a friend's crossbow. Hit her right in the heart. She jumped up, landed, and just looked around while two huge streams of blood ran out of her. She slowly walked away wagging her tail and tipped over in some brush. We waited 45 minutes for another one (nothing came in) and then went to retrieve the doe. She jumped up and ran off! We waited another hour and went after her, only to have her run off again. I came back bright and early and tracked her through 5 beds over a half mile before the trail dried up. She showed up a few days later like nothing happened, with messed up fur where the arrow went through.
Turns out the arrow was dull and she clotted up with just enough blood to stay alive. If we had grabbed her right away or after we jumped her, she would not have gotten away.