Our best guess is that Sanderson, and later Crucible Steel, served as import agents
https://docs.google.com/document/d/17ixogftgITEblNUWtmFBv96ZvgjK6eFell8GsAWd-KI/edit
Scroll down to the bottom for "Where Were My L.C. Smith Barrel Tubes Made?" by Roger L. Domer and published in “The Journal of the L.C. Smith Collectors Association”, Winter 2017

A few doublegun makers DID source tubes from Whitworth and Krupp pre-WWI
Winchester contracted with domestic steel makers, including Bethlehem Steel Co., Remington produced its own decarbonized and fluid steel barrels, and possibly J. Stevens.

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