Steel shot with a full choke

[bornhunter]

I shoot upland with an Ithaca model 37 feather light 30 inch with full choke and lead shot. If I want to shoot ducks with this gun will steel shot ruin it? I've heard modified only for steel shot?

[Widgeondeke]

 
I would avoid steel or Hevi-shot(very hard), but you may look into Bismuth. It is one of the softest non-toxic available. 

[bobcat]

I definitely would not use steel shot in that gun.

[T-Bone]

 
I would avoid steel or Hevi-shot(very hard), but you may look into Bismuth. It is one of the softest non-toxic available. 

X3...Cabela's has Bismuth. Steel shot. could bulge the barrel.

Mike Orlen can open the choke to anything you want at a very reasonable price (Modified or a Light Modified would be good) or buy a new barrel.

http://users.dls.net/~rdouglas/MikeOrlen.pdf

[bornhunter]

Ok thanks guys.

[boneaddict]

Besides screwing up your barrel, it doesn’t pattern well either and will decrease your success.  Bismuth is the best choice as far as I know

[Bob33]

https://www.quora.com/Is-there-a-legitimate-reason-that-a-shotgun-from-the-era-of-legal-lead-shot-not-be-able-to-shoot-modern-non-lead-steel-shot-A-gunstore-employee-said-to-my-friend-that-one-shouldnt-shoot-steel-shot-out-of-this-shotgun-Why

[huntingfool7]

The picture above is from shooting steel shot that is not contained in the shot cup.  That is not a normal practice and as far as I'm aware, all factory steel is loaded in steel rated wads.