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Checking for cracks
Unread 01-28-2020, 08:35 PM   #1
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Default Checking for cracks

Just looked at a Damascus steel barreled 1884 10ga gr 2 . It arrived in the mail while I was away at work so when I got home I was like a kid at Christmas opening and having an inspection first thing this morning. To my dismay I noticed what looked like cracks on the right barrel . The heart was pretty heavy as the only reason I bought this shotgun is to shoot Canada geese with it this fall. The seller was telling me that they were scratches however they looked very suspicious. I decided to stop into a Non destructive testing shop and they used a process called Ultraviolet Mag particle testing. They spray an oil based developer on the steel and in a dark room turn on the ultraviolet light. To my glee there was no cracks!
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Unread 01-29-2020, 09:11 AM   #2
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PHEW!!





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Unread 01-30-2020, 09:25 AM   #3
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That's sounds like a pretty sophisticated process to check for cracks. Glad to read that you got your goose gun. Go get em!
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Unread 01-30-2020, 05:12 PM   #4
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More than you probably want to know about Magnetic Particle Inspection (MPI)
https://www.nde-ed.org/EducationReso...principles.htm

VERY few testing labs have experience with pattern welded tubes, and interpretation of esp. Twist barrels can be difficult. A normal exam however would be reassuring





MPI is generally considered to be the best method for the detection of fine, shallow surface cracks in iron and steel, especially fatigue cracks. However, defects deeper in the material ie inclusions, may be missed.

It of course tells you nothing about the bore, and for that reason direct observation with a bore scope, and wall thickness measurements of any vintage barrel are needed prior to use.
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Unread 03-10-2020, 09:34 AM   #5
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Drew:

In the attached pictures - the top one: is the bright green line on the "top" barrel a crack ? Likewise, on the bottom picture, are the two bright green lines cracks (with the fine lines merely being normal features of twist barrels) ?
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Unread 03-10-2020, 09:43 AM   #6
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John: here is that barrel segment



and radiography of the segment showed no evidence of cracks. The 2 markers are the ? indicators on MPI. The small lucent areas are felt to be bore pits

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Unread 03-10-2020, 10:09 AM   #7
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I had my ca. 1886 Parker hammer gun (twist barrel) radiographed locally, but nothing conclusive was found, even though I see something that looks like it could be a crack in the bore. I had a guy with a local boiler company video the bores with his borescope, and you could see this "crack" - but it was hard to tell if it was a crack or merely just some corrosion along the lines where the different metal "strands" meet. (This gun is old & well-used. Even the outside surface of the barrels has some of that "washboard" feel to it, so I'm sure the inside surfaces have it too.) I wish I could email the video to you, but it is a 63 MB file. I did send the barrels to Merrington, for inspection, measurement & light honing. I hoped that the honing would remove this "defect." It did not. I asked Kirk about the "crack" - and he acted like he didn't see one; didn't know what I was even talking about. (Which made me wonder...) All he kept saying (instead of a direct answer) was "If it was my gun, I would shoot it with proper, low-pressure loads." It still makes me wonder what I'm seeing, and why he acted as if he didn't notice it...
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Unread 03-10-2020, 10:44 AM   #8
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My compliments for doing your due diligence John. I'm not aware of any NDT lab with significance experience in evaluating pattern welded barrels, and suspect it may be related to liability concerns.
It is my not particularly informed opinion that direct visualization, RT and MPI are complimentary. If MPI showed an indicator at the same location as the visible "crack" I would be apprehensive.

This is Jay Oliver's 1874 $100 grade Lifter with a fracture in the Crolle barrel probably at the rod edge "zipper" weld



A Twist fracture



Damascus-Twist fracture

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Unread 03-10-2020, 12:43 PM   #9
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Having more years, than I care to recall, with hands on experience, in MT (dry or fluorescent), RT, LP(V), LP(F) ET, and UT, I can say that if I were heading off to a Lab (many of which are run by my ex QC Dept, I would be asking for either Visible Dye penetrant, or fluorescent dye penetrant testing.
The very nature of Twist, Laminated, or Damascus materials is very conducive to false positive interpretation. The magnetic permeability of the dissimilar materials is distinct enough to show flux field lines.


The only important part of the above, for the non techs, is highlighted. I just can't help myself.
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