after a number of failures at making something like these I bought a mini bead lathe and did a small mod. took it's "tail stock" and removed the bearings. put an .500 x .325 nylon spacer. cut a small slit in the top of the spacer to make it fit in the 12mm hole. had to bore out the spacer after that to fit an .314 boolit. while cutting the spacer, I broke one end of it. became a blessing. gave me a place to hold the boolit while drilling.
I can see other uses for these tool. case trimming, spin polishing, with the right cutting, case forming.
the lathe
boolit
still a little off center
"tail stock" (12mm shaft support for cnc)