I've got one (modified NEI) mold for the .41 Colt on the way, and I'm waiting to see if I win the 386177 on ebay now. These are heeled bullet designs for the .41 Colt, base pour.
That heel needs to expand from .386" to .405" as the bullet exits the case and enters the forcing cone. I'll be casting of pure lead, but I'm wondering if there is a relatively easy (cheap) way to hollow base these bullets.
I'm thinking some sort of drill press based jig that would center and limit travel of a cutter in the drill press. That's all I have, and all my tools are basically woodworking tools, not machine tools.
Maybe it's my lack of imagination, but I can't imagine how this could be done in/on the mold, it being base pour and all.
Then, o'course, there's the question of: If it can be done, is it worth it?