Thought I'd add this here in case the thread came up in a future search.
By the mid 1890s U.S. makers advertised their pattern welded barrels as "Guaranteed For Nitro Powder"
Lots of information here regarding vintage shotshell pressures
https://docs.google.com/a/damascusknowle...fUOZEFU/preview Black Powder Pressures:
3 dram / 82 grains 1 1/8 oz. (1200 fps) is about 5000 psi.
3 3/4 dram GOEX FFFg with 1 1/4 oz. (1240 fps) is about 6000 psi.
4 drams of FFF (about 108 gr) with 1 1/8 oz. (1420 fps) is about 7000 psi.
"1895 Smokeless Powders For Shotguns"
http://books.google.com/books?id=Wv0MAQAAIAAJ&pg=PA446&lpg3 1/4 Dram/40 grains DuPont Bulk Smokeless 1 1/8 oz. = 7440 LUP
3 1/4 Dram/44 grains “E.C.” Bulk Smokeless 1 1/8 oz. = 7584 LUP
Note: Modern piezoelectric transducer measurements would be about 10% higher.
The 1963 George Herter "Reloaders Handbook" lists 23 grains (3 1/4 Dr. Eq.) of Infallible Dense Smokeless, now Unique, with 1 1/8 oz. shot in a paper case with paper wads (card & fiber) at 8,725 psi by LUP, or about 9,500 psi by modern transducers. (Courtesy of Mark Ouellette)
The 1933 edition of "Smokeless Shotgun Powders" by Wallace Coxe and E.I. du Pont de Nemours & Co. reported the LUP pressure for 1 1/4 oz. 3 Dram Eq. of DuPont Bulk smokeless at 9,600 psi.