I have several of Skennerton's books. They are top shelf! From the excerpts which you posted, I found the last section on Martini-Metford Percussion Locks for Ordnance, most interesting, and from the description of use, it sounds very similar to the American contemporary, Model 1885 and 1890 models of the 3.2" Field gun with the radial, then axial vent ignition methods. Thanks for posting, but we still are not making one. Let's say this, if you make the miniature authentic ammo to shoot in it, we will make the muzzle loader version in 1/6 scale. The ball is in your corner.
Tracy and Mike