16ga.com ~ View topic - Destructive and NDT of Pattern Welded Barrels

dyslexia strikes again Embarassed

I corrected my last post

drewhausemd@yahoo.com

Spoke again to METL about tensile strength testing. They need 4" of the muzzle end but without choke (to save on machining cost). SO it would save $ just to send what I need, but I'll want to document the maker and rough DOM. Depending on the amount of machning time to prepare the specimen, the cost will be $50-$70.

An update
http://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=357105&page=8

*Last edited by revdocdrew on Fri Apr 25, 2014 11:10 am; edited 1 time in total*

Some here have no doubt been following the thread on DoubleGun, but here is the short version of the Metallographic Analysis from METL, and my conclusions:

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 ignition 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.

METL now has 17 barrel segments (14 pattern welded and 3 fluid steel) for tensile strength testing, and the Hunter Arms Armor steel section will also have composition analysis so we'll KNOW what at least one c. 1900 tube was made of Smile

Very excellent. It is reassuring to know that the older gun makers made a good product and they had a lot of expertise behind what they built. I have always wondered if the bad press on "Damascus Barrels" was a market ploy used to increase sales of newer models.

Member Joined: 09 Jan 2013 Posts: 2170 Location: Florida

Very good info , Thanks for sharing with us !

I want to save some of the good stuff for the articles Wink

but progress is being made. Please see
http://docs.google.com/document/d/1ZIo0y746UsSRZIgRuuxwAbZjSBHitO_EanvwLYc-kGA/edit

and this might be of interest
http://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=357760#Post357760

As of now, it is my opinion that no one in this country has done enough radiography on pattern welded barrels to provide an expert opinion as to the significance of the images.
A VERY few gunsmiths are doing MPI, but even those finding are difficult to interpret.

I do think that the vast majority of pattern welded barrels can be adequately evaluated with:
1. Careful external and direct or fiberoptic internal bore inspection
2. Measurement of chamber length, forcing cones and bore
3. Measurement of the wall thickness of the chamber, forcing cones, 9" from the breech, 9" from the muzzle and MWT; measurements taken top, side & bottom
4. By someone with the interest, equipment, and expertise.

Recent tensile strength testing of Twist and Crolle Damascus barrels show an average of 54,000 psi or about half of the published industrial standard for AISI 4140 Chrome Moly gun barrel steel. For that reason I favor as MWT for pattern welded barrels:
End of chamber - .105"
Forcing cone - .100"
9" from breech - .040"
9" from muzzle - .025"
Factory original small bore guns however commonly have a wall thickness of .018” - .020” in the distal third of the barrel making it critical to use loads that ballistically match those originally intended for use in the gun.

PLEASE NOTE: no one can tell anyone on the internet or at the gun club if their gun is safe!