"hardcast'' IMO is a useless term, undefined. Or I have never seen it defined. So, to get the best results...accuracy and zero leading your bullet needs to obturate slightly to seal properly (gas cutting/leakage causes leading). First off you need to know the Bhn of your bullets. Get a Bhn tester, or read up on the use of drawing pencils to determine hardness. Cast Boolits forums is your friend here. Example...let's say you bought bullets of Bhn 15 (Lyman #2 alloy)...what pressure load do you need for Bhn 15 to go plastic and seal the bore? Constant 1440 x 15= 21,600 psi (not cup).
If you research your loading books that list pressure, like Lyman, you can find a load that will make your bullet work.
Unfortunately, to further confuse the issue, my experience is almost the opposite of Swifty's. When I have leading issues (very very seldom) I either increase the charge or go with a softer bullet. But, I am not operating at his speeds and pressures, and if you are on the upper end of power in your cartridge, I'd listen to him. I stay pretty much in the low to mid power levels...all my custom molds are built to drop the right dimension bullet of wheelweights and 5% tin...giving around a 12 Bhn. Mostly because my revolvers and rifles are well over a hundred years old and designed originally for black powder.
