doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Blow Up EUREKA

BTW: I would very much like to include Armory Steel used by American Gun Co./ Crescent Fire Arms Co. and Meriden Fire Arms Co./ A.J. Aubrey in the tensile strength testing.

METL Metallographic Analysis is in, and here's the short version. I'll let y'all know when/if the long version gets published

I believe the burst was caused by an obstruction, likely the shot wad from the previous shell, lodged in and just past the forcing cone, caused by a light powder drop in reloading and incomplete combustion from the very low temperature. There may have been a pre-existing bulge also.

1. Did the barrel fail related to low cycle fatigue? NO

The fracture surface exhibited a mixture of ductile overload (plastic deformation with both tensile overload and shear) and transgranular cleavage indicating a ductal failure mode with rapid failure. The cleavage failure appeared to form preferentially in the steel component. No evidence of fatigue failure was observed; there were no striations on the fracture surface.

2. Did the barrel fracture at a ribband edge weld, between iron and steel rod welds, or within a rod? NO

The fracture did not appear to trace along the ribband (spiral) welds. Some cracking was seen along the individual bands within the crolle pattern, but this was not always the case.

3. Did the barrel burst related to interlaminar rust, inclusions, voids, or embrittlement? NO

No evidence of embrittlement was observed. There were a large number of inclusions but there was no apparent fracture jumping from one inclusion to another. The composition of the inclusions was predominantly silicon, phosphorus, and sulfur ie. slag.
No voids or interlaminar rust were observed.

While the microstructure was banded, and the bands had different grain size, inclusion content, and inclusion form (globular in the iron and linear in the steel)... �the overall material appeared to be a single piece of metal...(without)...microstructural defects.�

Chemical composition was similar to AISI 1005 low alloy steel. The low range of tensile strength is 40,000 psi, but may be heat treated to much higher numbers.

Hi Drew,

Thanks for the summary. It's reassuring to know that these barrels are basically sound as opposed to all of rhetoric over the years about being an accident waiting to happen. It is interesting to note that failure did NOT occur at the presumed weak points.

Phil

Drew,
The test results that you have provided high-light the fact that the person that discharged the gun prior to the barrel failure was negligent; in that he/she failed recognise the potential risks involved when ever a weak/blooper discharge is experienced.
it should be standard practice for all participants in shooting sports, that when ever a weak discharge/blooper occurs the shooter must check to ensure that that the barrel is clear of obstructions prior to reloading and firing another shot."
The test results indicate that in the failure under review that this safety precaution was not followed.
Collectively we need to stress the importance of following the safety check described above in particular with every new entrant to shooting sports and for that matter some experienced sportsmen.

Drew,

Thanks for taking the time and going to the expense of having this testing done! The information revealed is invaluable to those of us who are fascinated with damascus barrels.

Thank you Doc Drew for your time, efforts and investment. Your investigation along with that or Sherman Bell and Tom Armbrust have gone a long way to dispel the myths surrounding the dangers of the use of firearms with Damascus barrels so long as they are in good condition and they are used with the loads they were designed for. Perhaps this will encourage manufacture's to start listing actual chamber pressures on their products.

Thanks guys, but there is ALOT more work to do. I think Adam's intellectual curiosity has been stirred, and hope he, Eldon and Steve will continue what has been started. We're already way past my cognitive capacity...and checking account
We should all be thankful to the guy who allowed the analysis of his blown barrel, despite the risk of criticism. Over the last 5 years or so there have been lots of posts on public forums about blown barrels, but no one seemed interested in actually finding out the cause. And many thanks again to all those who graciously provided knowledge or barrels, without which there would have been no NDT or tensile strength testing.

Steve: please think about visiting Paradise before the 2015 Las Vegas show and spending some time with Adam at METL!

Drew,

I will definitely be continuing work and research on damascus barrels. I am very interested in communicating with Adam and would like to come down for a visit. At the very least he should have my email address, in case there is any information that he may need to know about the forging process. Please feel free to provide my address to him.

I remain surprised at the very low carbon content of the tested barrel section. The chemical analysis essentially states that the two components are two different grades of wrought iron. I based my assumptions on the carbon content of the "steel" component of damascus barrels, largely on the writings of Greener. But also from writings in the French language, where the barrel components are referred to as acier (steel) and fer (iron). I remain reluctant to make an industry wide statement about the materials used, based on this one test result. I will look into having chemical analysis done on other barrels, to have more results to compare.

Thought I'd apply Barlow's formula to the subject barrels



The chambers are 2 5/8" and the wall thickness at the end of the chamber was .119". Estimating the OD is difficult so did ID + wall thickness X 2. This does not include the brazed flats which obviously provide significant additional metal/strength to the breech, but the barrel blew out laterally.

SO Barlow's formula P = 2 x S x t / D
P=Bursting pressure in psi.
S=Tensile strength of material in tube wall.
t=Wall thickness in inches.
D=Outside diameter in inches.

Burst pressure = 2 x 54000 x .119" divided by 1.053"

And the number is only 12,205 psi?!?! What am I doing wrong?

Chuck's calculation on p. 4

My SWAG is well in excess of 15K psi. Say 25,000 psi.

1) I base this on my estimation of the strength of the Damascus being around 60,000 psi ultimate, providing for mild steel being around 64,000 psi, and ductile iron being around 60,000 psi and some conservatism.

2) I used .100 as the Min Wall

3) A hoop calculation of a .798 I.D. chamber and .100 wall with a 60,000 psi strength is around 15,000 psi.