I appreciate all of your comments and kind words. I especially appreciate Tim's comments about the treatment of the lock panels...thoughts like those pry me out of the rut I've been comfortable in, and make me look harder at study pieces. I invite you all to critique this fowling piece, if you will. It can only benefit all builders.
The barrel on Leatherbelly's gun was made my John Getz. The barrel on my Chambers' PA fowler is a Long Hammock 46" . The octagonal breeches on both are within .015" - almost 1 1/16". The muzzle wall of the Long Hammock barrel is .100" while the Getz barrel is .140". but the Getz barrel has a little more of a flare. So, I'd say John did not contour the barrel to 20 gauge specs, but rather created a true 28 gauge fowling piece barrel. There is enough steel in the muzzle of the barrel to accommodate rifling, and I think Leatherbelly will mostly shoot ball out of this gun, so the heavier barrel will be a blessing.
Regarding John Schipper's engraving book, and I don't mind giving him a plug here....indispensable!! His easy way of writing is most welcome, and his detailed instruction will set up anyone with the desire to give it a try, to success. I think the thing that most impressed me about his style, is the fine-ness of the detail. The overall impression is great coverage, but the details are very small. The book has hundreds of examples to study, and reminds me in part of the European engraving books of the 18th and19th Centuries. The book encompasses a man's entire lifetime of study and presents it in easy to see and understand format. It is one of the best book purchases I've been able to make. Leatherbelly's gun just happened to be the one on the bench when my copy arrived, so it was my Frankinstein experiment.
He's coming over after lunch today to pick it up.