Dgang,
Well, if you have a revolver with the bore constriction that is common where the barrel screws into the frame, you may find you get better accuracy from softer bullets that do upset some. Upsetting back up to bore diameter under pressure after passing through a constriction cuts down on the gas cutting that causes leading. If you are shooting about anything else, hardness offers a means of resisting pressure deformation. That becomes important with rifle or other higher accuracy loads. The problem is that for 9mm at 33,000 psi, observing this limit already has you shooting Linotype. You can try doing that, just to see what it does to accuracy for you, but for lower pressure pistol loads you find BHN 16 handles about 20,000 psi. Super light 45 Auto target loads at 14,000 psi will work with BHN 11 without deformation. For magnum revolver loads, it just doesn't seem cost effective, and you are not shooting sub-moa groups with them, for the most part.
The late Richard Lee's book, Modern Reloading, 2nd Ed, on page 134 has a table of BHN vs. firing peak pressure. He set that firing pressure -10% lower than the alloy deformation pressure to provide a margin that allows for shot-to-shot pressure variation. It turns out to be a simple linear equation. To satisfy the zero deformation condition, your alloy needs to be:
BHN = psi/1280
or
psi = 1280×BHN
Edit:remove the irrelevant decimals.