I was in St. Marys, Pennsylvania in late December of the past year (mostly warming up from a somewhat futile early morning, deep-snow hunt for snowshoe hares). While killing some time haunting the local gunshops (with tightly controlled expectations!) I ran across a French gun that looked very much like a Darne(I can't recall the maker just now, it wasn't Bruchet either). It seemed to be very well made and looked like it might have some potential for adoption until I got it into enough light to see down the tubes. Egads! It wasn't pitted, it was cratered! How the exterior and action of the gun could look so presentable and the tubes could be so deplorable was a stunner for me. It has to be the metallurgy. I simply don't see better-made guns from other nationalities having such a problem.
