I have a Greener Martini in 12 bore rifle, and had to have a sizing die built to hold the .732 dia bullet- Fosbery style. This die sized down about 1/4" of the case neck to hold and center the bullet. BTW, if you are interested, the fella that made the mould still has the cherry, and could likely build you one as well. If interested, PM me and I will dig out that info for you. I have good luck using Universal Clays.
Thanks, Doug