We've all seen tests where a man wearing a vest takes a hit from a .44 magnum and barely reacts. I've also seen a test where a reporter volunteered to wear the vest and the shooter suprized him by firing a 38 to the mid section while he was still talking. The reporter ended up staggering back several steps and falling on his kester cussing and squaling like a child.
That in no way is representative of actually being shot. The energy of the round isn't being used to pierce bone, tear muscle, or expand. It's all being directed into a vest.
I've seen a video of a man taking a 308 WIN round from a rifle straight into the chest while standing on one leg. He doesn't move a muscle. People move from the shock of getting hit, they get startled. Again, from Newton's laws if it seriously had enough power to actually cause that person to fall over it would knock you on your butt too.