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Old September 3, 2008, 12:55 PM   #10
James K
Member In Memoriam
 
Join Date: March 17, 1999
Posts: 24,383
Hi, Unclenick,

Sorry, but it is the heat that does it, not bullet expansion from the pressure. The heat comes and goes very fast (not even fast enough to discolor the bluing) but it is there.

Have you ever fired a bullet at a steel plate (yes, I know you shouldn't) and observed the way the steel splashes. It looks exactly like those high speed pictures of a drop of water hitting the surface of water. Same crater, same "crown" appearance, same drops spashing up. For one instant, that steel and that bullet were so hot that both the bullet and the steel plate actually melted and splashed up when the bullet's kinetic energy was changed into heat. The only difference between the steel and the water is that the steel absorbed the heat quickly and "froze" while the water just flowed back into the crater.

That is also how armor piercing bullets work. The bullet strikes the steel and the heat causes it to become, for an instant, like a soft putty that the hardened carbide core then penetrates. If the steel is too thick, it will absorb the heat causing the surface to solidify before the core can penetrate more than a few millimeters. The result is seen in tank armor where a machinegunner has fired AP bullets at the tank and they are stuck in the armor.

HTH

Jim
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