I'm just stating opinion here. When steel first came out many gunmakers advised NOT using it in the old fixed choke guns. I believe it had a lot to do with thin poor quality wads used in early steel loads which allow the steel shot to contact the barrel and the fact that steel shot is much harder than lead and when forced through a full choke, which many of the fixed choke guns were, had the potential to bulge the barrels particularly if large shot common to waterfowling was used.
In the early to mid 90s I shot a fair amount of steel through a 70's erra Citori with full and mod chokes and never experienced a problem. I did restrict shot size to #2s and checked my wads for shot burn through which I never found (though it was common in the 80s').
But like I said it's just my experience/opinion
