Neither all lead, nor all copper is created equal in terms of hardness.
Minimal to no expansion in "hard cast lead" bear protection handgun ammo is almost standard thinking.
Seeing firsthand the scrap pile of material that didn't make the cut, in Steve's garage was a major point in my willingness to give all copper bullets another try.
Manufacturing techniques such as swaging (Barnes) also work harden at inconsistent rates in my opinion.
My recollection the "OriginalBarnes" were pure lead and copper, I know they're soft", and generally heavy for caliber,
The HP on the Hammer has also evolved larger. Sucks for BC, but makes terminal performance reliable in lower ranges, and as yet no upper limit has been found. offsetting this by running lightweight to 4000 fps makes for as ButterBean says a "game changer".
Blowing shoulders of large bovines with projectiles a third the size of what was previously considered standard is real.
Work on HP depth is ongoing.
Ive been hardcore, esbigger calibers, heavy for caliber bullets has been my position for 4 decades, but occasionally an old dog learns something new.