I found a post by Researcher that according to Charles Semmer, a few late production 12G higher grade guns were barreled with
Krupp Fluss Stahl tubes. Dave has examined a D grade.
https://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=483651 Should have started with this
http://parkerguns.org/forums/showthread.php?t=23586 The 1878 E. Remington & Sons catalog listed the $45 hammer lifter double with Decarbonized Steel; with Twist for $60, and Laminated Steel for $75.
“The barrels of this kind of gun are made from decarbonized steel containing only enough carbon to give great strength combined with toughness…This steel is now largely used in gun work, and is much stronger and reliable than the cheaper kinds of twist found in many of the imported guns. Indeed, some gunsmiths prefer it to any twist, and claim that it makes a better shooting barrel, owing to its being perfectly homogeneous. In the manufacture of these barrels, they are rolled from the solid metal, without welds…The steel for the manufacture of the plain steel barrels is used in the form of round bars…rolled out to the size required…”
“After the barrels are rolled, they are bored out, then turned and ground, and proved with a heavy charge of powder and a solid slug of lead.”
