I shoot lead anywhere from 10-17 BHN, and if the bullet fits the gun, I can run them up to Magnum velocities with no leading (the 10 BHN). For mebbe 13 years I didn't even consider BHN and only cast wheel weight alloy, it's equivelent, or range lead. Fit is much more important. Today "hard Cast" is used by manufacturers to satisfy/make sales to new users who think "harder is better", and as stated above many commercial casters use hard alloys to keep the bullets nice and smooth during shipping. At one point I tried the "formula" regarding bullet hardness vs chamber pressure, but weren't worth the effort, to me at least...