Oooh! I'm extremely interested in this! Any chance someone could translate for the english speakers? Babelfish is not quite up to par
Madbull makes 6mm .43g BBs, if you're looking for something heavier than .30g.
Where did you get/how did you make the barrel? How does it compare accuracy/consistency wise to a hop up system?
It would probably work even better with something like this:
https://secure.airsoftcanada.com/showthread.php?t=65541