I asked Barnes about spin rate vs expansion. This s what I got back.
" In theory increased rotational speed will damage more tissue, but in reality it is such a minor amount it would be very difficult to even detect it. There is a maximum rotation speed, for most bullets, jacket bullets can and sometimes do come apart in air if they are spun too fast. The Barnes bullet�s the all copper bullets cannot be spun to fast to come apart so as far as function it cannot be spun to fast, as far accuracy is concerned, spinning them too fast can be detrimental to accuracy. We have not seen any indication showing that jacketed bullets open wider because of rotational velocity, but with the all copper bullets we have seen enough evidence to suggest that they do not open wider due to the rotation of the bullet."
Bluntly then, at least in the case of Barnes bullets increased expansion due to increased spin rate is wishful thinking. Whether there might be increased tissue damage due to increased spin rate if we radically increase spin rate remains open but in doubt because of the probability of accuracy loss.
Maybe we should think about building a test rifle to see what happens. Right now the rifles we use them use copper bullets in are designed primarily for cup and core bullets and not exclusively for copper. Some of our barrels are very fast twists, but not into the range where just copper can handle to RPMs yet.
