Jean-Baptiste Delcour-Dupont (later Canons Delcour) of Nessonvaux also used the 'Crowned D'. His mark has been found on damascus and steel brl Smith and Fox guns, and may be a more likely source for the Lefever brls.
Sanderson Steel was started in England in 1776
http://www.sandersonsteel.com/200_years.htmSanderson Bros. Steel Co. started their 'Syracuse (N.Y.) Works' in 1886, and supplied Nitro and Crown fluid steel brls to Hunter Arms starting in 1895. Halcomb Steel Co. opened in 1905, and L.C. was on the Board of Directors. Halcomb supplied London steel for 0 grades and Royal steel for the hammer guns starting in 1907. Crucible Steel Co. bought Sanderson Bros in 1900, and Halcomb in 1911. Parker Peerless steel may have come from Crucible also.
'C' and 'S.B.&Co.'