I think we have several similar threads going on right now in this same subject.
I loaded and shot thousands of hard cast, Keith style, SWCs from my .44 mag. over the years. I loaded them at all velocities, never have had a leading problem, ever. Mine were commecially cast (Oliver bullets, out of business now) so I cannot repspond to the comment about different kinds of "hard" bullets. These were good. That is what I know.
I never gave the barrel special de-leading treatment and it shot rifle-accurate up to the day I tore up my shoulder and had to stop shooting it regularly.