Every deer that I have ever shot with the 70 gr. Barnes TSX (with a .223) was DRT - Dead right there. They have taken a collective total of ZERO steps after the shot.
Shot placement probably has the most to do with expected performance verses actual performance. I have taken a Bobcat through the neck at 386 yards (as well as another on at 10 feet), and deer from 120 to 160 yards. Every shot was an instant, incapacitating kill. I have never recovered one of the bullets, but field dressing the deer shows large wound cavities and traumatic damage throughout the wound channel.
Since I launch my favorite bullet at a relatively modest 2750 fps, I wonder how much bullet velocity is playing in these failures that other hunters have noted. My meager cartridge does not send them to the target at the scorching velocities that I hear others quoting.