jawjadawg,
"Buchsemann, can you explain how these fatigue fractures would have occurred? Would one possible cause be the use of high pressure loads? The barrels might not have failed catastrophically at the time of use, but instead formed tiny cracks which then accepted moisture, leading to rust?
Do we all need to get out the microscope to take a closer look at our barrels?"
Rather than writing a lengthy description of how fatigue fractures come about I'll keep it short by saying such is caused by cyclic/repeated stressing and relaxing or loading and unloading of a material. The failure begins with a microscopic crack and over time the crack continues to propagate until the material finally lets go. The "beech marks" that I noted are trace evidence of this process having taken place though I personally haven’t viewed such in Damascus steel. I too noticed the impressions in the plastic hull which reminded me of an oops experience I had working up a regulation load for one of my double rifles. In short I zigged when I should have zagged with my powder charge and almost destroyed a rather expensive weapon and did bodily harm to my person. In addition to temporarily freezing my highly re-enforced action, stretching the material of the receiver to its upper limits (the gun had to cool a little before the cross-bolt released), the machining marks in the chamber where imprinted about the exterior of my brass case.
Again, I am no expert but it looks to me as if the exploded gun pictured in this thread has seen more than one heavier than necessary charge.
I like Damascus barrels and see "quality" tubes as being just as good as nitro barrels and far prettier when loaded correctly. IMHO the series "Finding Out for Myself" written by Sherman Bell is a must read for any early shotgun enthusiast; thinking a good idea for any "gunny" really.
Mark
PS - If you are concerned about the state of your barrels with regard to fatigue there are many materials labs scattered about the country, manned by "experts”, that could do some simple penetrant tests and other visual inspections for you to put your mind at ease. PM me if you want to go that route.
