doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Myth of unsafe Damascus still alive

Thanks for posting the photos I was referring to. Did you notice the way the brass on the fired shell appears to have flowed into the extractor cut and the way the primer is protruding from the shell head? I think that this lends strong credence to the overload theory, however, the barrels do seem awfully thin in the area where the forcing cone should be evident. At any rate one or a number of bad things contributed separately or in conjunction with each other to cause the only unintentional damascus barrel blow up not attributed to an obstruction I have seen.

Doug;
I did find those exact pictures in the picture trail linked above. Maybe you just failed to scroll on down far enough.
PeteM;
Thanks for the vote of confidence, but I believe I have learned more from you on damascus than you have from me. Personally I consider you one of the Experts in the field of Damascus barrels.

Pete: Have you ever thought of being a politician? Your answer to my question re 'rust between the welds' was absolutely evaded. Bill Clinton couldn't have done a better job of dodging the question. And you are right too about all the bullshit here. But unlike some of you, most of us do not have a PhD in physics or metallurgy and we are just trying to understand this damascus conundrum in layman terms. So Pete, since you are an expert, I'm asking you again to scientifically prove to us that rusting does not occur in the welds of Damascus steel, particularly that which is over 100 years old.

Buzz, you are asking an impossible question no one could answer in the way it is phrased. The closest anyone could come would be to report observations. Theoretically, it would be possible but I have never personally heard of such an occurrence. I have seen/read of instances where corrosion (pitting) has penetrated through a barrel but cannot recall of any being directly linked to a faulty weld.

"not pictured in the picture trail link posted above"

Apparently an internet epidemic of psychologic scotoma.

St. Augustine
It is no advantage to be near the light if the eyes are closed.

Exactly. So Damascus really is by definition a bit of a conundrum. Most Damascus barrels are likely safe and this was established with Sherman Bell experiments trying to blow them up. But, are there any unsafe Damascus barrels out there and if barrel walls are thick, ie greater than .020" can it be unequivocally assumed that these barrels are safe? I'm not 100% sure on this? I think a good experiment would be to take a nice big lot of these barrels and do a cross section analysis under an electron microscope and examine these barrels for rust. One would have to use trashed barrels because who would want to ruin a good gun in the name of science. But to me this would be a good scientific experiment. Has anyone ever taken a look at these barrels in this manner?

What would that really prove, Buzz. To be meaningful the sample would have to be huge. And even at that it would still not represent the whole. And I would imagine a series of any barrel metal would result in discover of many variables--steel, damascus, laminated, etc. In all respect for your inquiry I think you're debating something that has no answer or value.

Well......how else would one be able to test as to whether rust actually compromises the Damascus welds or rather if indeed this is all myth?

Bro. Buzz.

There was a call on the DoubleGunBBS and PGCA sites in 2005 "Contribute Junk To Advance Barrel Strength Knowledge" with the hope of obtaining vintage barrel samples for composition and strength testing. This was posted by �Zircon� in 2007. Unfortunately, the testing effort apparently ended thereafter.

http://www.familyfriendsfirearms.com/forum/archive/index.php/t-55364.html

January 2007

I am doing a failure analysis of a pair of Parker barrels - one set damascus, and the other set homogenous Vulcan �fluid steel�. These barrels were used in the study by Sherman Bell and Tom Armbrust, published in Double Gun Journal. They subjected each barrel to increasingly heavier loads and they both failed at about 30,000 psi. Modern ammo gets up perhaps to 12,000 psi. Most folks that shoot these old gals use shells loaded to the 7,500 psi range.

During the failure analysis I noticed that the fracture length for the Vulcan barrels was substantially longer than for the damascus barrels. A close examination of the fracture surface showed progressive, low cycle fatigue marks on the damascus barrel. The crack advanced slightly with each increasingly higher pressured load. On the Vulcan barrels, both sides failed by a brittle fracture mechanism. By this, I mean the barrels let go in one fell swoop. Even though both sets of barrels failed at 30,000 psi, the behavior of the damascus barrels was superior to the Vulcan barrels, owing to the fact that the Vulcan barrels failed in a brittle fracture mode. A ductile fracture trumps a brittle fracture every time.

One of the (myths) with damascus is that it will fail at the welds where the original rods were forge-welded together. When I looked at this particular set of damascus barrels using a metallographically prepared sample, and up to 1,000X optical magnification, I saw NO EVIDENCE of weld joint failure, slag in the weld joints, porosity in the weld joints, etc. I have about 30 old barrels in this study, homogenous, damascus, and twist included. I am a practicing metallurgist who holds an M.S. degree, and am qualified to state the observations of barrel integrity made in this posting.

On the two old Parker barrels, there is a screw hole that comes up from the bottom and pins the extractors in place. Both barrels failed at that hole, because it takes a (segment) out of the side of the chamber and is the thinnest portion of the chambered area.

The damascus barrel let go by a mechanism known as low cycle fatigue. Each succeeding round had higher and higher pressure. After several rounds, a crack started at the extractor screw hole. Each successive round caused the crack to open up just a bit further, until finally the overpressure could not be contained and the (barrel) failed in a ductile fashion. Ductile failures in steel look like a taffy pull at about 1500 to 3000X magnification using scanning electron microscopy. There is a cup and cone appearance with a lot of micro-voids present. This appearance is a dead-set giveaway to a ductile fracture.

The "fluid steel" barrel failed by brittle rupture. The fracture surface is more or less smooth, but has some "rivulets" in it that point back towards the initiation point, which again was the screw hole. The fracture surface was about 3X as long as for the damascus barrels. In other words, the same 30,000 psi final internal load created a lot more fracture surface in the homogenous barrel than in the damascus barrel. This indicates that, for an equivalent-length fracture, it took less energy to open up the homogeneous barrel than for the damascus barrel. The words in the Sherman Bell article were that the Vulcan barrel failed much more abruptly and (violently) than the damascus barrel.

So the verbal description of the failures during firing and the visual observations of the fracture surfaces are in accord with each other. Both barrels ripped lengthwise for some distance and then the rupture terminated in a circumferential crack. In the case of the damascus barrels the crack spiraled around with the weld pattern, but it was not on a weld, rather it was on one of the in-between areas. After the damascus pattern is formed by wrapping rods together and forging them into a strip (the "skelp") which is wrapped around a mandrel, spiral paper-tube fashion, and is forge welded together. These spiral welds remained tight and the parent metal is what failed. This may seem pretty amazing, but in many, many instances the actual steel welded structure is stronger than parent metal.

Many microphotographs, chemical analysis of the steel, etc. (will) make up the (anticipated) article. I'll also be looking at several other barrel ruptures and measuring the strength of the various barrel steels in the "hoop" direction as the barrel will always fail in hoop tension with a lengthwise crack. Any internally pressurized cylinder has 2X the force in the hoop direction as in the longitudinal (axial) dimension, so it's no wonder why barrels all seem to blow out with lengthwise cracks.


TSI Inc. in MN performs industrial metal testing, and has evaluated a limited number of pattern welded barrels http://www.tsi.com/

Drew: Thank you for that posting. That study was clearly in support of Damascus and a great start to testing ESP by a metallurgist. He states there were 30 barrels but from the statements it appears only one Damascus and one steel barrel was actually tested. The best study designs are large studies with comparison group. I think you are right and it was unfortunate that more testing wasn't done after 2007 to really get to the bottom of this. But I agree with you guys in that I believe most Damascus barrels with thick minimum barrel walls are indeed safe to shoot.