The SAAMI spec's for shotshells were developed as a standard for the ammunition industry to go by for the safe maufacture of ammunition for use in nitro-proof barrels.
Here's a link;
http://www.sportsmensclubofcliftonpark.org/docs/shotshell_pressures.pdf
Barrels are tested beyond the pressure limits established by SAMMI and are proof marked.
The ammo I shoot in mine are 10,500 psi loads the SAMMI spec is 11,500. An overpressure is not likely to occur unless the shot column meets a restriction in the barrel.
The choke is a restriction. The more open the choke, the less restriction you have.
I fail to see the logic of "just because you've gotten away with it, Doesn't mean you should do it" I feel, based on hands on experience, that if you are going to have a problem, it's going to present itself quite quickly,
and that is a possibility you should always keep in mind. Also as a point, I too own guns that I won't shoot steel in.
I said in the earlier post, the decision is totally yours and and shouldn't be approached without
careful consideration. There is no definitive yes or no answer. Many problems with early steel no longer exist. Some are still there.
And if it makes your hunting buddies feel better, have 'em hide behind something for the first few rounds.