Ken:
Well, I called Bob, who obviously knows his stuff, and had a very nice conversation and he gave me lots of pointers. Then he wondered if I had asked Lightfield if they sold reloading components for their 16 gauge sabot slug. And of course I'd never thought of that approach . . .
So then I got on the phone with Mr. Fritz and - yup - they sell slugs and sabots for reloading.
Thanks for pointing me in the right direction.