How much of the recoil is due to the high speed gases exiting the gun. I ask because isn't that how muzzle breaks work? Don't they direct the high speed gases backwards, so that instead of a certain number of grains (same weight, remember) of gas flying out the front at 5000 ft/sec, it goes to the side, and thus produces less recoil?
Furthermore, technically, to knock someone over, wouldn't you just have to dump enough energy that thier center of gravity got off balance, and they fell over? Think about it this way, if someone catches a soccer ball mid chest (and holds onto it), and is not well balanced, he will probably be knocked over. Wouldn't the same principle apply with a bullet? Of course, that assumes that
1)The bullet dumps all its energy in the person
2) THe bullet dumps all that energy in a short amount of time
2)The person is off balance.
I would say that those qualify as rather big assumptions.
And the important thing isn't that someone gets knocked over, its that they can't get up again. And thats a whole different ball game, and frankly, is much more important then wether someone can get knocked down.
Just some things to think about. And no, i don't put much stock in "knockdown power". This is just my "know nothing" opinion.