This might clarify things
Black, Bulk & Dense Smokeless Powders, and Dram Equivalent
http://www.shotgunworld.com/bbs/view...?f=13&t=455407
Phil: there is a (limited) list of factory published and tested shell pressures at the bottom here
https://docs.google.com/document/d/1...UOZEFU/preview
As to "What loads should I use in my Pattern Welded barrel" see toward the bottom
https://docs.google.com/document/d/1...vwLYc-kGA/edit
The easy answer is "Loads for which the barrels were designed", and we now know the pressures of those loads.
I believe Pattern Welded barrels without defects and with adequate wall thickness may be used with
pressures similar to that which modern loads would generate. That said however, I DO limit shot weight and FPS for lower
recoil in light of the now more than 100 year old wood and lock-up.