It’s not molten, and heat plays no role in the penetration ability. This is a very common misconception.
It’s simply focused kinetic energy that does it. The cone focuses the copper into a slug like object, and the slug becomes similar to an extremely powerful bullet.
So it's like that old picture of the grass straw driven through the telephone pole by nothing but hurricane wind?
The flimsy straw could do it simply because of how fast it was moving. The strength of the straw doesn't matter, simply it's mass, moving that fast, carries itself through, ie the leading edge is not being pushed from behind like a nail, more like a bullet with a string attached?
Setting aside the simplification, that probably the mass of the rest of the straw does play some part not absolutely zero, is that a reasonable way to conceptualize it?
Are you certain that a hurricane can blow a straw through a telephone pole? I hadn't heard of this phenomenon and was interested. I was unable to find a good source.
According to this article, the National Oceanic and Atmospheric Association thinks it's not possible:
The picture (perhaps multiple but at least one) was a piece of hay poked right through a telephone pole, in the aftermath of some kind of storm. Not a tree. It was shown in grade school in the 80s or late 70s.
It’s really hard to get a slug
Moving like that without tearing it apart. It’s easier to use the explosive to spread the force over a wider area initially but in a way that the projectile is formed by the concentration of the explosive forces mashing it all together. Weird.
It’s simply focused kinetic energy that does it. The cone focuses the copper into a slug like object, and the slug becomes similar to an extremely powerful bullet.