"Hard Cast" was (is?) a product line from Rem for magnum handgun ammo, and featured a flat pointed lead bullet, typically heavy for caliber, intended for handgun hunting and slightly higher velocity than typical lead bullets. The slugs in the "Hard Cast" line have a flat point, sort of a wide flatnose shape.
Hard cast is also a term used in reloading and bullet casting to describe a slug that is notably harder than average lead bullets. I am not a bullet caster and am not going to try to describe further.
"Round nose" is a bullet profile or shape. Thus a round nose slug could be hard cast. (or put another way, cast harder?).
Slugs with flat points have long been thought of as better game and SD bullets from big bore revolvers. The classic semiwadcutter is such an example. Round nose lead slugs are typically not thought to be as good for game or SD.
That said, big bore RN lead bullets from a .44 spl, .45 LC or even .45 acp FMJ. are thought to be acceptable SD rounds, but SWC or truncated FP would be a mild improvement.