A human's body reacts to being shot the same as an animal. If you shoot a deer or a hog with a high powered rifle, they might run off or drop to the ground, but they never get blown backwards. I watched a science show about ballistics (so I know it is true) and the explanation was the actual force of the bullet on a body (besides penetration) was equal to the kick from the rifle with some allowance for distance. That is why a victim would typically fall over or slump.