Many Moons ago on the old, old TV program "You Asked For It" (with Art Baker as the host), they demonstrated a vest with a Police Officer firing a .45 ACP into the company President's chest with a Thompson M28-A1 from about 12 inches away and it didn't even knock the ashes off of his cigar.
That's because the vest (nylon only in those days, Aramid fiber or Kevlar was not invented yet), was thick enough with the ballistic weave to distribute impact.
Even today with the modern plastics ceramics and metal plates, there is still enough shock (depending on the weapon of course) to knock a guy on his butt. Perhaps it is more surprise than actual Kinetic Energy. But the idea is to put the guy down in a more vulnerable position and momentarily incapable of shooting back. Therefore the more reflexive action you will experience such as spinning around, falling down, flipping backwards, etc. It's a natural thing that you cannot get out of a dead pig.
Just 3 weeks ago I was invited by a company to examine some metal inserts they are designing for personal body armor. They were wondering if Navy type Class A armor would work.
Well, the rest of the meeting and my comments of course are confidential, but the fact remains; the bigger and faster the slug the more damage you will receive.
One thing I didn't tell those engineers at the meeting: Though their inserts seem to be the best I have ever seen, I have a small Naval Cannon at home (built the carriage myself) with a 1 1/4" bore. That not only would knock down Bigfoot wearing one of those vests but probably break a rib or two at the same time.
