"Back 'shortly after the requirement became mandatory' he wasn't hand loading steel because there were no components.
PSI is PSI and it matters not what the payload is.
SAAMI max is 11,500 PSI for 3" 12 gauge.
You have no idea what pressure factory shells are loaded to, lead, steel, or anything else unless it's stated.
'Thinking I had nothing to lose'. Taking a 1907 gun out to 3" and feeding it early factory steel is certainly an interesting experiment.
Glad both he and the gun survived... that would have been way outside of my comfort zone."
My reference to steel shot shells being light loaded was indeed a reference to the weight of the payload. I still have 3" lead loaded "magnum" shells from that period with 1 7/8 oz payloads (and recall 2 oz loads as being available also), while the heaviest 3" steel shot loads obtainable at that time were 1 3/8 oz (which load I was shooting). What I recall was that 3" magnum lead loads delivered punishing recoil, while recoil from those 3" steel loads seemed to be more or less equivalent to normal skeet loads. I don't recall shell pressures being published, but fully realized that shell manufacturers deliberately maximized velocities to compensate for the fact that lighter steel shot pellets shed velocity much faster than the same size lead pellet. And although I did shoot thousands of hand loads in those days (to include my Damascus guns), I was oblivious to pressure concerns; and don't recall period loading manuals publishing pressures, only velocities. We obviously have vast amounts more knowledge and data these days, and have further benefited mightily thru the ability to share data and experiences on forums such as the double gun shop; but this venue and the web were non-existent when steel shot was first forced upon us shooters. As to this particular Fox gun, it locked as tight as the proverbial bank vault, and there was more than sufficient wall thickness to handle the lengthened chambers (Buck Hamlin checked wall thickness and lengthened chambers); had this gun and barrels been otherwise, I would not have risked my fingers. Although I strongly suspect many posters to this forum have conducted myriad experiments themselves, the steel shot experiment described above (as well as other ideas I've tinkered with in years past) was my personal version of "finding out for myself"; and I'll never say anything other than mine was a very favorable result. But I also clearly stated in my original post that "I certainly wouldn't recommend someone do the same with his gun", or take any unnecessary risks; for with the volumes of excellent information and resources available nowadays, there's simply no need.
