Our American double gun manufacturers all bought the rough tubes from various suppliers, and then made them into barrel sets. Over the years I've seen both Sterlingworth and Chromox Fox barrels with the marks of the various tube suppliers --
LLH is the mark of Lochet Habran of Jurille, Belgium.
Three-lobed crown over a D = Didiere barrel works of St Etienne, France.
The SB&Co. mark = Sanderson Bros. & Co., a Sheifield, England, company that set up a branch in Syracuse, New York. I have found Sanderson Bros. & Company ads in old Syracuse city directories.
