Originally Posted by Drew Hause
Long splits without a ring bulge (usually with lifting of the rib of a SxS) are almost always from thin barrels.
I asked the metallurgical engineer at METL who supervised one of my failure studies how much the wall thins with stretching before bursting and his answer was "not much".

[Linked Image from photos.smugmug.com]

It should be noted that thin walls alone should not be blamed as the cause of long barrel splits, or other failures. In the Preacher's photo above, we see what are generally considered "thin walls" all along the barrel split. But note that we see wall thickness dimensions ranging from as high as .027" and no less than .019"... and these numbers are AFTER stretching to the point of rupture has occurred.

If "thin barrels" was the cause, then someone has some explaining to do. Assuming these barrels have been fired and survived many hundreds or even thousands of shots, why did the failure take so long to happen? Since we see a fair number of Flues guns with fairly thin barrel walls, it's safe to assume those walls were just as thin 10-20- or 50 years ago.

Common sense would dictate that there had to be some combination of factors that led to the presumably sudden failure. Perhaps it was a light obstruction such as a wad or snow in the barrel. Maybe there was some internal flaw or inclusion in the barrel steel that held for decades, but finally let loose with a single round that produced slightly higher than normal pressure. Something may have scored the inside of the bore creating a stress riser that became the initial point of failure. We don't know if this barrel suffered any prior damage such as a dent, or even what the temperature was when it failed. We can all engage in guessing games, but with the information we have, nobody really knows. Metallurgical testing might shed some light on it, or maybe not.

What we do know for certain is that there are many thousands of guns with even thinner barrels than this that are still being used with both low pressure and standard factory field loads. But they have not had this sort of rupture happen. The Preacher himself has stated he owns an O grade L.C. Smith with Damascus barrels that have a thin spot measuring around .016" at roughly 14 1/2" from the breech, as I recall. Yet those considerably thinner barrels have not failed even though the thin spot is closer to the breech where pressures are presumably higher. The Preacher uses low pressure loads in this gun, but many other guys are blissfully firing any old factory load through guns that have barrels with points just as thin, or thinner.

There are many factors that may determine that a barrel will fail under normal use. If it was a matter of barrel wall thickness alone, there would be no need for any sort of factory or government mandated proof testing. All that would be needed is a minimum allowable barrel wall thickness. I'd bet the London or Birmingham Proof House could tell us about a great many barrels that failed proof even though they had what would normally be considered very adequate minimum wall thicknesses. Unfortunately, steel is not some homogenous monolithic substance of 100% consistent purity and identical properties. In a sense, I suppose we could safely say many barrel failures occur because of thin barrels relative to the pressure they were exposed to and other factors.