I've held off on this one, wanting to read some of the responses from others because this one can get very complicated & also quite heated.
We all go off of personal experience, the more experience, the more chance for failure, success & opinions that can be flexible or maybe 100% based on just 1 or 2 shots. If they were good it's a great bullet, if we made a bad hit or missed it was the bullets fault, just human nature.
I personally don't think there are any bad bullets, I just think they can be used for the wrong situation & bad things happen. I've heard stories of the shot being absolutely perfect yet the animal escapes & is never recovered, how do we know it was a perfect shot if we don't find the animal.
Use any bullet outside it's parameters & bad things "might" happen, sometimes we get lucky & it still works out. I'll give you an example.
Back in the very early 70's me & a friend were deer hunting & we had tied our horses in the shade next to a nice little Beaver pond (full of trout) & started hunting a stand of Quakeys. We spotted some deer but didn't shoot anything & it started to get dark. On the way back down I happend to look up on the skyline & spotted a spike bull elk. If he hadn't been sky lined I never would have seen him.
I had an elk tag in my pocket but was packing a Ruger 6mm with 85 gr. Nolser Solid Base bullets because I was deer hunting. I had won the rifle the year before in a big bull elk contest, it was one of the very first flat bolt 6mm's ever made.
The shot as I remember was about 80-90 yds steep up hill & I held on the base of his throat. At the shot he disappeared & neither of us could tell if I had hit him or if he had ran. we walked up hill but now it was dark so we walked back down to where I had shot from & looked again.
We spread out & went back up & my buddy Gene stepped right on his legs. That Nosler Solid Base, against all odds had killed that bull, wrong bullet, light caliber & a full blown lucky shot.
So, what makes a bad hit, many things. Bad shooting, wrong bullets, too far away, sometimes too close & the bullet explodes on impact. Bad angles can do it, hunting isn't written in stone, once we pull the trigger lots of things can & do happen, some are good & some are bad, some can be explained, some can't, some are imagined.
Then there are times the perfect bullet is used & put in the perfect place but the animal actually over powers the bullet, yes it does happen. You do everything right & still it takes 3-4-5 shots or more on a Cape Buffalo, Elephant, Lion, etc & still the animals soaks up bullet energy long enough to put up a fight, there's enough oxygen in their system to stay up & be a danger for a long period of time. Nothing is guaranteed in hunting, nothing.