If you had access to a lathe, you could make a new piece for the mold. Thats what I did with a Lee mold, the .575 minie. Its not made as a shotgun slug. I made a new base piece that shortens the skirt to get the right weight. Simply filling the base would make them a bit heavy, all the solid slugs are pretty short. I think its a bit of luck to find the right wad for this use. I bought some Fiochi bulk 20ga, opened them up, melted the shot into buck or slugs, and re crimped them. The slugs do pretty well. But another brand, they were all over the place, just the difference in wads.