I use an old model 12 for the small amount of waterfowl hunting I do and I use bithmuth shot. As stated above in a fixed choke gun with constrictions tighter than improved cylinder, there is a real chance of swelling the barrel or even splitting it.
No, not steel nor most non toxics. Bismuth or similar "Soft" non toxics are OK, but best to get an Express for waterfowl and keep this fine old shotgun for other stuff.
I have a model 12 that I do shoot steel through, but it is cylinder bore with a Polly Choke on it. I will not shoot steel in any of my choked model 12`s.
Thanks! This firearm has a lot of family value, so I don't want to damage it. This was my Wife's Grandfathers gun. I thought it would be cool and nostalgic to take it bird hunting. No problem. It is a fine gun for clay birds.