Wal Winfer's book British Single Shot Rifles, Volume 5, Holland and Holland has a chapter on the Paradox guns including reference to the 10 bore. The chapter has line drawings of the 8, 10, 12 and 20 bore bullets. They are all pretty similar. There is a dimensioned drawing of the 12 bore bullet.

You might want to contact Mr. Winfer and see if he has a drawing. He is in Australia.

Is CBE making your bullet mould, they make a quality mould.