A few BR shooters load their 220 Russian with 224 bullets when fireforming their 6mmPPC. They do it in their old 6ppc barrel or 6ppc fireforming barrels.
I just use a case full of Bullseye and a wax plug. I do fireform my 30BR brass in a 6mm barrel. I drill the bore for about 4" with a .302 drill and chamber with my 30BR reamer. I do not do my fireform with a bullet.