Illustrating the concept
A reader sent me this link to an old Richard Davis "Second Chance" video. The video has Davis shooting a fellow - who is wearing one of Davis' vests, of course - with a .308 rifle and himself with a .44 magnum revolver. The reader's comment was "if this doesn't show an energy dump, I don't know what it shows."
I agree. With the second part of the statement, at least. Going back to our "Stopping power" series, as I pointed out the term "energy dump" is nonsensical - energy isn't "dumped", it is used to do work.
What is the work in this case?
First, I can guarantee that the bullet itself was grossly deformed in its contact with the vest material. It takes energy to deform the bullet, and that energy only comes from one place: the bullet itself.
Second, there is a huge amount of work being done by that slug. It is trying to part and sever the fibers in the vest material, which are quite tough and designed to resist such force. The bullet does manage to defeat some of the fibers - which is why it's buried between the layers of cloth - but the energy required to do that job, again and again (there are many layers in a vest) rapidly depletes the bullet's stored energy. The result is that all of the energy is used up doing the work of penetrating the vest.
Again, the bullet's energy wasn't "dumped" - it was used. Understand the difference, and terminal ballistics won't seem so mysterious.
(Notice also the second myth busted in the video: that a bullet has enough energy to knock a man down. As you can see, even full-power .308 NATO, at near contact distance, isn't sufficient to knock over a man standing on one foot. Again, there is nothing mysterious at work - simply basic physics.)
-=[ Grant ]=-