To me it is not as simple saying keep it no bigger that no. 2 and all will be good. Unlike you guys I have seen quite a few vintage shotguns damaged from steel shot especially in the early days when steel was new and guys knew no better and just took their old guns and fired them unaltered
Belling of the barrel was common and we actually had a few split in the choke area even though they were opened up from full and many had severe barrel scoring
Most of the damage the owners didnot even realize it was happening nor do they today IMO unless a big bulge or split occurs
An issue in the past was the poor quality of the steel shot wad which allowed the scoring of the barrel and the big one was the poor grade of steel pellets being used in the factory ammo which after a trip or two out into the rain or salt air started to rust up or bond togther within the shell to the extent almost a slug was created which did a lot of damage
I don't shoot factory steel only steel reloads but if I was I would want to make sure exactly what is in the rounds I was firing to make sure they have a quality wad that protects the barrel. That is easy to see, just pick a few up after firing to see if the pellets worked outside and keep a eye on the barrel for scoring. Also make sure quality plated shot is used to ensure they cannot bond together since un like lead there is no give
This was damaged with steel shot that had no give and bonded together
For me if I was to fire steel out of a vintage shotgun , open the choke as required and fire only quality plated steel ammo with good wads that protect the barrel. I would be suprised if some of the cheaper steel factory loads have both even today
Vintage guns that have any value to me will never see steel shot regardless if safe or not
Just my 2 cents
Cheers
