Yes - aware of the work-hardening of copper and/or guilding metal.

What Rod's experinents showed, though, was that the cores didn't separate, not from the Bonded cored bullets, lead still 'stuck' to the jacket material, and in the standard drawn cup, swaged ammo, the ones that did separate merely fell apart after stopping, not during the trip.

I'm quite 'taken' with these 'reduced' bullets.