Haven't killed all that many deer with a muzzleloader. Maybe 10 or 12 total. They all were shot at under 100 yards (some much under) with bullets ranging from 250 to 300 grains pushed by 80 to 100 grains of powder. All shots have been in the "boiler room" and all but one dropped in it's tracks! The one that ran was already running from other hunters and made the mistake of stopping to look back. It went about 30 yards after the shot.
I have also shot a few deer with a .45 Colt pistol (Ruger - and I had hot reloads with 250grcast bullets in it) and none of them went more than a few steps.
I agree that a big heavy bullet lumbering along at slow to medium velocity is all it takes - IF you put it in the right place!
BTW - One of those deer with the .45 revolver was running and I led it too far. [
]The bullet hit it's neck, broke the spine, and the buck's head dropped and the antlers hit the ground causing it to do a complete flip. It never moved again! Not a shot I'm proud of, but the results were still good with that big heavy bullet.