I often hunt upland game where non-toxic shot is mandatory. and sometime use one of my vintage SxS's. I have used 12 gauge #3 and #4 steel shot in "open-choked" older SxS's, with zero problems to date. I do not use steel shot in barrels tighter than modified.

I do use bismuth shot in the full choked barrels (at $3 per shell!).

JERRY