I go through lots of range lead. Most range lead will include jacketed bullets, plated bullets and cast bullets. For me, hardness runs 8 - 10 bhn or so.
For low power loads, I tumble lube with a made at home mix (BLL). Since a required BLL ingredient is hard to find, I would recommend 45-45-10 from White Label Lube. Tumble lube is a lot easier than PC and works fine for 38 special.
For mid range to full power loads I use PC. This has included 327 magnum, 9mm, 357 magnum, 357 maximum, 7 TCU, 30 Herrett, 44 magnum.
I water drop out of the mold for convenience, not hardness. I do not worry over the 15 minutes at 390 deg F that gives my HF red a good cure.
Why are you worried about hardness? Unless you are talking about very special applications, any bullets made from range scrap (air cooled, water drop, or water drop + PC) should work fine for all the more common uses of cast bullets. For avoiding leading in a 38, bullet fit is much more important than hardness. Undersized bullets are the biggest cause of leading in revolver loads.