CBE here in Oz make a .410" - but with a gas check.
http://www.castbulletengineering.com.au/bullet-moulds/rifle/40-calibre?Page=2&Items=12

Dave also makes the 310 cadet heeled bullet as well so maybe that could be at least a starting point for you?

What is the cartridge you're looking at Casper - you have me intrigued!