Leonard also built the A. Hollis double rifles as well as many if not most of Jeffery's. The hallmark of a Leonard firearm is a 3 or 4 digit number on underside of barrel just under the fore-arm. I am working on an article about Hollis double rifles and Leonard as builder for DGJ. As far as we can tell, Leonard built complete rifles and guns for Hollis and Jeffery. Not sure if engraving was done by the retailer of by Leonard, but the Leonard and Jeffery rifles we've studied are identical.
Bob