Your cast bullets should not have any mould halve fins on them. They should look like they have come from a CNC machine. The fins are 'adding' to the diameter of the bullet(s) and are causing the brass to bulge (according to what you have described). You are also attempting to correct a problem that will not go away with the use of the Lee Factory Crimp Die. This die is not intended to be used with cast bullets. You are swaging the cartridge (and the cast bullet) down to a lesser diameter. Fix the cast bullet problem first, stop using the FCD for cast bullets, and get the Lyman 2 Step M Expander Die to properly prepare your case mouths for cast bullets. You will be back in the ballgame once you have achieved this.
Dardas Cast Bullets