One of the interesting points that your access to the Jeffery "daybooks"(workbooks) will identify is who actually made their Jeffery N.E. Double Rifles. The Rusty Knight & Mark Cash & R. Nolan Keiler research showed that Daniel Leonard & Sons made a significant number of the W.J. Jeffery (& A.Hollis)
N.E. Double Rifles. A number of good Birmingham gunmakers made guns "For the Trade" for Gun Retailers in London or overseas either "In the White" or as "Finished Guns".

Chris C