I've never done this before, but I've read about it in the ABC's of Reloading. I would think if you want a good hollowpoint, you need a lead that is not way soft, but not too hard either, probably a Brinell rating of 14 or something like that. I wouldn't want to cast it where it's going to have a hard time expanding.
That's all I've got. I'll keep an eye on this thread too, you never know when you might need to acquire this skill.