I've been loading 40 cal bullets in brass 410 cases(converted from 303 Brit) for a while. I use 38-40 data, without a wad. I bump the casemouths down using a 10mm sizing die, and seat them just like a regular metallic cartridge. This works well, but I also wanted to load plastic shells, with the same data. This will only work with a 0.410" slug that fits snuggly in the case. Well, I came up with a way to both bump the diameter up, and put flutes on the slug. Right now this crude, but I do plan on making a die to do this as soon as I can borrow a lathe and tool post grinder, or tool and cutter grinder.
What I do is push a Lee 401-175-TC through a twelve point 9mm wrench. It goes in 0.4012" and comes out 0.4096"
To load I toss the powder in a primed hull, then tamp a small piece of tissue on the powder. This just holds it against the flash hole. After that I thumb the slug(with just a small bit of lube on it) in place, and use a 45 acp taper crimp die and Lee spindle and 303 Brit shellholder in a drill, to iron the case mouth out, and crimp the slug in place. It works kinda like a roll crimp, but it puts a taper on it instead. The lube melts a bit and sticks to the plastic, and helps hold the slug in place. I have also loade a cew that I moly coated. I haven't tested them yet. I am still testing fot accuracy. So far I've not put it on paper, but I have shot soupcans at 30 yards, behind my house.
To see the images I guess you will need to go to Cast Boolits. I'm using an android, and I don't see any way to attach them.