If the shotgun has a full choke I would not use steel shot .Especially if the shotgun had any age to it.
Depends what you're using. If it's an older wingmaster, it probably has a pretty thick barrel on it.
I wouldn't use t's and stuff like that...but, you shouldn't anyway.
Use 4's & 6's for ducks with steel loads.
Doubtful it will hurt your choke at all...
People compensate the steel for lead by using bigger shot sizes (t's, bb's etc) and it doesn't work that way.
Lead kills with "impact".
Steel kills with "pattern".
I've gone to 4's and 6's and have been knocking more ducks down. The more little pellets you can throw at them, the better chance of getting more head/neck shots....hence...more ducks.
In this I'm also saying in all liklihood, you won't do any damage to your fixed choke either...