I have cast and used hollow based .395 minnie's for my 40 cal. "Turner Kirkland" squirrel rifle.
My molds are Lee but the base pin is seperate and has to be placed in the mold for each minnie. The automatic style would sure speed things up.
I use 100% lead or as close as you can get with lead pipe. They shoot a nice group if you use a heavy lube in the grooves, not as tight as a PRB, but close. I have "barked" squirrel with that ball many times.