Sirs;
At a certain amount of pressure brass becomes like plastic, steel becomes plastic to the point even that lead (softer than steel) will "penetrate" steel! Now, it seems to me that it is a measure of molecular motion and I guess you would call that "heat."
How can soft lead penetrate hardened steel? Heat - molecular change brought about by a facility/friction/heat!
How fast does it happen? -nanaseconds!
Steel, or any other molecular substance under heat will deform - jet aluminum aircraft allow, 4140 steel - some people calll it metal fatigue - it can happen fast with a bullet ringing a barrel or slow with a jey losing a wing!
I never thought about "heat" ringing a barrel till Jim clarified it, but thinking it through he is technically correct (as usual - darn it).
Harry B.