John,
I am not familiar with gunsmiths in your area that would or wouldn't be knowledgable on old doubles. Most gunsmiths, I fear, are afraid of Damascus and Twist guns because of the liability they may incur. If you google
https://sites.google.com/a/damascusk...e.com/www/home you will find great information on these old barrels. Toward the bottom of the page in blue is Barrel Evaluation which will give you what you want to ask the gunsmith to look for.
Kindest, Harry