Three years ago, I had a Winchester 23, which was originally bored full and modified, opened to Modified and Improved Cylinder by Mike Orlen. I use the gun shooting ducks and geese in Canada and the East Coast.
It has had a couple of flats of 3" high velocity #2 steel loads through it and I have no issues.
I did this because I prefer a SxS and there is no way I am putting steel through my Model 21 or through my Ithaca NID Mag 10. Besides, I like my Model 21 to much to trust it to the tender mercies of the baggage apes when I fly.