doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Wall thickness measurement

Dewey Vicknair's blog
https://vicknairgunsmithing.blogspot.com/2020/03/mechanical-wall-thickness-gauges-are.html

DeFelsko PosiTector UTG P1
https://www.tequipment.net/DeFelsko/PosiTector-UTG-P1/Ultrasonic-Thickness-Gauges/

Steel measuring range 0.008" to 0.475"

Dewey is free to his opinion, but documentation that the newer ultrasound devices are more accurate than the pin and gauge tools would require comparison of both techniques on multiple barrels.

When Bill Henry made my tool, he also made a standard segment of .038" thickness with which I could 'zero' the gauge, and could (and do) recheck frequently during the measuring process. If my gauge has been set to the .038" 'zero', repeatedly measures the wall thickness at the same number (say .045 at 9"), and when checked is still set at .038" I believe the measurement is accurate. Flexing of the round support bar does not seem to be relevant to the relationship between the pin on the bar and the pin of the gauge, unless I contact the barrel wall with the bar.




The use of Ultrasonic NDT is an entirely different issue. Scroll down about 1/2 way here for a summary and links
https://docs.google.com/document/d/1ZIo0y746UsSRZIgRuuxwAbZjSBHitO_EanvwLYc-kGA/edit

I can't comment if the new high resolution US devices can detect defects within the wall of fluid steel or pattern welded barrels.

The problem with RT is in differentiating surface defects (pits) from defects within barrel



A few smiths and NDT labs have examined pattern welded barrels, but there are no industrial standards for the interpretation of those tests.
Both MPI and RT might be helpful to show microscopic through cracks in a pattern welded tube.
Obviously a great deal of research would need to be performed to determine if US can find hidden defects/voids/inclusions in pattern welded tubes, but the industrial money is not in testing a few vintage shotgun barrels.

Bottom line: if you want assurance as to the safety of your barrel, beyond a bore scope exam and expert wall thickness measurements, have them proved at a pressure of 1 1/2 X the pressure of the load you intend to use. And there are testing labs in the U.S. that will do that.

I remember a recent thread in which a member found to his horror that the minimum wall thickness of a gun made for him in Europe in 1972 (?) was only 7 thou.

Assuming that no work had been done on that barrel since it was made it appears to have survived both Proof and just on 50 years of at least intermittent use without even bulging.

As there is no definite minimum thickness at which a barrel will/will not fail it is perhaps less important to worry whether the gauge is producing a reading to the nearest thou, than to regard what it shows as a “ball park” figure to show if the minimum figure is adequate, marginal or “buyer beware”.

Hosford's tutorials from 2009 are still on youtube

would be nice to hear from members here, re their opinions regarding minimum barrel wall thicknesses in front of chambers, for modern fluid steel barrels...

I use a cheapo one from Brownell's and my measurements have been confirmed on Hosford or similar gauges. I simply allow the gauge to flex vertically before/while zeroing the gauge.

The measurements don't need to be precise, I just need to know within a few thousandths what I am dealing with. The thinnest I have seen so far was my 12 proved 10 gauge that had been hogged out to a .783 bore. Still had .021 at the thinnest spot.

I have a spring on mine that keeps pressure on the pin. repeatability is key I use mine vertically and recheck it a couple times

dan, telling us what the thinnest measurement is, is of little value, without telling us where that thinnest point is...

and barrel wall thickness in front of the chambers and perhaps incremental measurements 16 inches or so up from there, is what is really important for safe shooting...

mc, what gauge are you using? Have you used any method other than "vertical"?

Has anyone on here used an Ultrasonic Thickness Gauge, other than Mr. Vicknair?

Any recommendations for an Ultrasonic Thickness Gauge other than the referenced $1,395.00 gauge?

Thanks in advance!

I have never used one to measure shotgun barrels.

They are commonly in use in industrial piping environments.

Because, when things flow through a pipe, they wear it out from the inside, leading to leaks, big, and small.
So, they are pretty common.

I’ve seen two types, one type connected to a computer screen, and one type just touched on the surface.

On the computer screen one, the operator move the transducer back-and-forth, and identified very precisely where the voids were behind the surface.

What I am trying to say, is that the people using the tool are not super geniuses, but the tools work very well, so the learning curve isn’t long, and doesn’t require complex fixturing or technique.