Is Bismuth the only shell that can be shot from a Nonsteel gun.

Besides the obvious of lead, Bismuth and Kent Matrix (which is some kind of pressed tungsten powder) are the only two that I know of that are recommended for older shotguns. The founder of Bismuth died, and someone else started making them, but I'm not sure of current availability. Same for Kent Matrix, it's still available but I'm not sure of current production.....I'm not saying they aren't currently making it, I just don't know for sure. I've shot some bismuth over the years and it worked reasonably well. I haven't tried Kent Matrix but it looks good on paper.

Steel won't normally really destroy an older gun barrel, but will possibly cause a pressure ring just behind the choke, especially if it is a tight full. It should not be used in most older doubles or any guns with significant value, monetary or sentimental. If you really want to hunt ducks and can settle, I'd suggest spending a few bucks on an 870 or a Benelli Nova, both of which will handle steel or other modern hard shots easily and are usually pretty good handling and functioning guns.