9.3's are .366" in diameter. I use to use a "draw down" die made by Corbin to "draw down" .375" 220 grainers to .366" and shoot them in a double rifle i have. (i also retailed them) It worked quite well. I do have a bullet mould for .366, but i forget what brand it is?? I think it's NEI???
You could use a luber sizer and .366" die with, .375" soft round balls. Just force them in to make a soft .366" diameter "shootable" bullet. It will pull off a lead ring that won't go into the die, and you just discard that.
Just a bit of terminology here... You "swage" something to make it "bigger" in diameter... You "draw" something down to it a "smaller" in diameter..
Drilling Man
Edit: BTW, very nice rifle.. Hope to hear more about it when you get it!