doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com THAT was close

Jager: can't confirm that, but at the failure analysis the metallurgist can tell the difference between rapid ductal failure (plastic deformation with both tensile overload and shear) and fatigue failure (striation 'waves in the sand').

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.

In the 70’s apparently “fatigue” followed by inevitable failure was a “fact” among a segment of the shotgunning public. Thomas, in his book of that period, “Shooting Facts and Fancies”, speaks to the concern in a section entitled, “Do Guns Tire?” and references an enquirer’s concern that a “considerable number of old guns … were coming to the end of their life” due to fatigue. He quotes a “well known” shooting writer (whom he leaves unnamed) who supports this position, “Metal tires with age and use, and becomes subject to fatigue.”

Thomas’ answer? “That is putting things in the woolliest possible terms, and as a general statement is simply not true.”

“… it is not age that induces fatigue in metal, nor is it use, as such, but only repeated stressing above the fatigue limit.”

“The thing that limits the safe life of any good, honestly-made gun is not the fair wear and tear it has had, but outstandingly the abuse or neglect it may have suffered.”

And in conclusion …

“The number of guns of all ages and grades that fail in normal service, other than those that have suffered abuse or neglect, or improper repair or some obstruction in the barrel, is utterly negligible, and the possibility of their so doing is well inside the margin of acceptable risk.

So herein is our dilemma. We may be able to see signs of neglect or abuse but we can’t “see” how the 100+ year old arm that we are shooting was stressed. We can’t know the internals of the metal used in that specific gun. And the designers and makers of these guns themselves didn’t know the fatigue limits of the guns when they made them.

So as I currently await the arrival of a “new” Damascus barreled double I can’t know what it’s experienced in its 121 years. I can only thoroughly inspect and measure it once it’s in hand and then make a determination as to whether it falls within my own “margin of acceptable risk.”

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Rocketman
"Age (chronological time) embrittlement is not an issue with plain carbon steels such as used in older fluid compressed steel barrels, twist, and damascus. Fatigue embrittlement would require millions of cycles at the level of strain which barrels in good condition experience with firing."