I'm with you Bigbulls, theres no such thing as knockdown power. A hand thrown baseball hits about the same as a bullet. I've seen deer drop with an arrow by a lung shot, and Ive seen them run a 100 yds from a high powered rifle. Some run some drop.
My buddy dropped in his tracks from a .25 shot to the groin, said his legs just gave out.
I dont think there is any REAL formula for why some deer drop and some do not. I know it has nothing to do with energy or the size of a bullet. I have seen tiny bullets drop them, and seen them run also. It's funny that everyone here drops them in their tracks with their ( insert caliber here) but in the real world I rarely see them just drop, unless its a head, neck or spine shot. Sometimes they do, I grant you that, but most run a little ways.