There are guys that want to shoot real heavy bullets (300 grain) in the 44 mag
I have a 320 grain plain base mold and it shoots very accurately. Granted I mainly shoot that bullet in my Ruger Super Black Hawk. I don’t see the need to spin the bullets faster?
I mainly shoot cast bullets in my pistols and revolvers and maybe 50% in my rifles/carbines.
I did have a problem with an early Marlin 444 and that cast bullet shooting accurately. But I didn’t play with sizing the diameter to fit that micro groove barrel (or really much dinking with the load either) as I only had one sizer for the 44 at the time. The bullets went straight into the target but they were not close together.