"Hard Cast" is many times just a marketing term used to sell bullets to shooters that think harder is better. Bullet fit is the key to shooting clean, leading free bullets. For revolvers, bullets the same size as cylinder throats works very well. For semi-autos, .001"-.002" over groove diameter is good. IMO, bullet fit is more important than BHN (I've shot some over max. loads of True Blue in a .357 Magnum (oops!) and 140 gr. SWC cast from wheel weight alloy, mebbe 10 BHN with no leading because the bullets were .359", cylinder throats are .359", and groove diameter is .357". No idea how fast they were going but I'd guess at over 1300 fps).
Slug you cylinder throats and barrel and size, or purchase, bullets accordingly, same diameter as cylinder throats...
My Anchor is holding fast!