Mark,
Benelli, Franchi, and Beretta are all the same company (think GM).....I would purchase a choke tube that is specific to Hevi-Shot or Heavy Weight (Federal).....You can use a plain lead full, Imp. Mod, or Modified.....When we patterned Hevi-Shot the best pattern at 40 yds was Imp. modified (heavier & denser than lead).....Stefanie shoots a lead full for her turkeys in her Benelli M-2 20 gauge.....I do believe the choke tubes are the same for a newer Franchi Afiinity.
If you want, we can try them at the NWTF Spring Turkey Tune-Up.