I agree CD, a cannon ball would probably be good for "knock-down!"
A 2X4 to the head would be knock-down power too!
But, bullets have already done their jobs, before the deer can think about running!
It is hilarious on TV how when someone gets shot, it picks them straight up, and then throws them backwards!! Only in Hollywood!
In reality, (unless you hit heavy bone) neither the human body, nor deer have the density to provide enough resistance to a speeding bullet, so as to "knock them down." So the animal either drops, or runs.

Now for the next part of the debate, a "complete pass-through" or a bullet that transfers all its energy, and does not exit.
It gets tricky here too! I prefer a complete pass-through, with the RIGHT amount of bullet expansion. Some might argue that this is "wasted energy." Whereas a bullet that has stopped, utilized ALL of it's energy in the animal.
Maybe yes, maybe no. With the wrong bullet, a pass-through can be terrible, no expansion, no blood trail.
On the flip-side the bullet that stopped in the animal, did it expand too quick, and "explode" on contact? Or was it under-powered and did not pass through?
Again, I prefer the complete pass-through, with a GOOD bullet! It delivers just as much as, and in some cases MORE energy, than the bullet that stopped inside the target!

Again, "knock down" is a MYTH, except in bowling and boxing!