I would have thought if faster twists make cup/core bullets expand more, it would do the same with copper bullets, to some extent at least. After all they are all metals.
I can hear the howls of derision because my opinion is not based on 37 experiments with 4000 data points: "Experience trumps opinion every time" etc etc.
Anyway whatever reason someone goes onto an internet forum, I didn't come on here because I am a scientist. But most good experiments have their origin in mental experimentation.
All I can add is: cue the soaked newspaper test.
