A muzzleloader bullet --- especially a round ball --- causes allot less hydrostatic shock than a similar weighted bullet that is shot from a hi-power rifle.

Here's another poster --- 'Beekeeper' --- from another hunting forum on this disputed subject:

"I hit a buck like that once bowhunting and it didn't kill him. How do I know?

Because a buddy of mine shot the same buck 30 days later with a rifle during gun season. My arrow did very little damage to the buck's lungs (just a small amount of scar tissue) and the X the broadhead had made on pass through was plainly evident on both sides of the chest wall.

The arrow passed between ribs ribs partially severing one on exit. The external wounds were scabbed over. Whitetailed' deer are tough."