From 1893 - 1895 Parker Brothers Gun Co., Remington Arms Co., and Hunter Arms Co. all began using some variant of “Bored For Nitro Powder” in company advertising, as eventually did other U.S. makers including Baker Gun & Forging Co., Ithaca Gun Co., J. Stevens Arms & Tool Co., Hopkins & Allen Arms Co., and Crescent Fire Arms Co.
Sears, Roebuck & Co. declared in 1907 that “Every gun we offer for sale (many of which had Pattern Welded barrels)...is made to stand any proper load of nitro or black powder...” and the “Our L.C. Smith Hammer Guns” listing included the statement “Choke bored for black or smokeless powder” and “NOTICE: All our guns are tested with heavy loads and cannot burst except by carelessness, obstruction in the barrel or improper home loaded shells with nitro or dense powder.”
“Our L.C. Smith Hammer Guns” in Sears, Roebuck & Co. 1907 Catalogue No. 116 courtesy of Gary Rennles
These statements of course apply only to loads for which the gun was originally intended. The standard 12 gauge loading listed on L.C. Smith hang tags from 1887 until about 1920 was for 1 1/4 ounce of shot with 3 Dram Equivalent of powder (1165 feet per second/fps). The 12g standard was changed to 1 1/8 oz. after about 1920. 16 gauge (introduced by Hunter Arms in 1896) was for 2 1/2 Dram with 1 oz. shot, and 20 gauge (introduced in 1907) was for 2 1/4 Dram with 7/8 oz. shot.
Nobel’s Explosive Co. Sporting Ballistite for shotgun shells was released to the trade in 1895, and 12 gauge 2 5/8" 1 1/8 oz. 3 Dram Eq. (1200 fps) Dense Smokeless powder loads were reported to have a Lead Crusher Pressure of almost 3 Long Tons (UK) per square inch, which would be about 9,500 pounds per square inch (psi) if measured by modern piezoelectric transducers. Dupont or Schultze Bulk Smokeless were about 1000 psi less.
The maximum recommended 12 gauge load listed on 1908 Remington hang tags was for 1 1/4 oz. shot with 3 1/4 Drams (1220 fps) of Bulk Smokeless or 26 grains of Infallible or Ballistite Dense Smokeless. (Courtesy of David Noreen.)
Lots more infro, and c. 1900 American maker's ads here
https://docs.google.com/a/damascusknowle...ZhIiY62Hx4/edit 
