I found these when I was searching for info on barrel inserts for shotgun barrels. What I was looking for, and what I think I found, was inserts like Krieghoff offers for their drillings. Of course, Krieghoff only offers inserts for their own guns, and only on new ones from the factory. Has anyone worked with or used these inserts? I'm considering a Merkel drilling in 12x12x9.3x74 but I wouldn't mind the ability to get a second shot.

http://www.keppeler-te.de/cms/pages/englisch/hunting/insert-barrels.php