Copper flows under the pressure created by impact, not as much as lead but it still flows, otherwise it would not expand.
And I would expect its expansion to be influenced by the spinning rate, probably not as much as with a cup and core projectile, which does happen, but I can�t see why it would not be affected.
It would be an interesting test... Hopefully, with so many short and long twists rifles in .224 calibers around, someone will find the time and take the trouble.
Alvaro
