Joe, having worked with dozens of old barrel sets over the years this is a first for me too. If I offered a guess as to what allowed this condition to develop it would include neglect and quality of the forge welding but it would be just that; a guess. Lab analysis might uncover what happened but there's no need for that. This artifact is over a century old and simply has seen better days.
Bibbyman, as we all know you rarely find a Damascus barrel pit free. If you do chances are it has been back bored. I have built several double flints using barrels with moderately pitted bores that are perfectly safe and pattern well. As for value, my friends double has no real value other than sentimental. It has been in his family four generations and says he has the perfect place for it.
In summary, these barrels are dangerous and unsafe under any condition IMO. So, to remove all chance of mishap we'll plug the chambers and weld them shut. One may ask "Isn't that a bit much?" As Mark Twain once said "It's better to be careful 100 times than to get killed once".
Hank
