I can cite a good example of bullet failure. An acquaintance of mine took his 6" Colt Python on a hog hunt. His first shot was an easy broadside shot, maybe thirty to fifty yards. The boar was pretty big, around 350 lbs. His ammunition? Remington factory load .357 Magnum 125 gr. Semi-jacketed Hollow points. When hit, the porker turned and looked at the man, and another shot was fired, the pig ran, changing directions with each shot. This man emptied his Python, reloaded and fired three more shots before somebody put a 12 ga. slug into the boar and the animal "passed."
An autopsy revealed all nine perfectly expanded bullets just under the skin in the top layer of fat. None had penetrated to reach vital organs.
I shot one hefty ground hog hitting just above the rectum and the bullet exited just under his chin, pulling most of his intestines out through the exit hole. This with a .44 Magnum using a 245 gr. Keith cast bullet.