Late to the party here but..are we certain that there was not some obstruction in that Flues tube? Maybe I've missed something but most of the destroyed shotgun tubes that I've ever witnessed personally (& thankfully not experienced) were caused by a wad or dirt or even snow (which is what wrecked the last 3-inches of my brother's 16 Nitro Special back in the late 1970s).
Embrittlement arguments have been around for a long time and yet they've never been explained in a way for me that is convincing. There are many really old automobiles and even aircraft still in use that would also be subject to this malady and yet they are still in operation.
