Minimum Wall Thickness at Point of Proof

[Jon Hancock]

What is the general consensus when it comes to minimum safe wall thickness on a Damascus bbl at point of proof? I know this is a loaded question but looking for opinions.

[Jon Hancock]

Never mind. Found a good thread on this already.

[Dean Romig]

Please share the thread here so others can read it.

Thanks, Dean

[Rick Losey]

at point of proof? .



just curious - What do you mean by that?

a distance from the breech?

[edgarspencer]

I'm with Rick; I am not sure I understand the question. Are you asking for a min wall thickness, at the point where the wad/shot charge would be when the highest breach pressure is occurs?

[Dean Romig]

And to further muddy the waters, what gauge? As the bore size decreases the working charge pressure generally increases - minimally of course - consequently, the minimum wall thickness becomes more of an issue.






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[Bob Brown]

Under the British rules of proof, the gauge is determined by a bore diameter measurement taken 9 inches from the chamber end of the barrels. All measurement to see if it is still in proof are taken at that point so I think that is what they call the "point of proof". I called Graham Greener with a question on a shotgun and asked him what he felt was the minimum safe wall thickness for damascus barrels and he said 25 thou., others might say 20 thou. Everyone has to decide on their own number for minimum wall thickness. I think I read somewhere the Birmingham proof house would often refuse damascus barrels submitted for reproof when the minimum wall thickness was less than 20 thou,. but that would partly depend on what the original proof was done at.

[Rick Losey]

well - true - the bore size is determined - as stated by the Birmingham house
"(ii)
Each barrel shall be gauged at a distance of 23 centimetres from its breech face for its bore diameter, which shall be
within the limits set out in Table 1A ofAppendix I for the diameter of such barrel. "

but that is strictly for determining the bore size - that states nothing about the wall thickness at that area.


20 thousands 9 inches from the breech would scare the heck of of me :eek:

To quote Mr Greener from our recent converstion
" Barrel wall thickness measured 9 inches from the muzzle end of the barrels should not be less than twenty thousandths of an inch. But the policy, of most gunmakers, is not to sell guns with barrel wall thicknesses less than twenty-five thousandths of an inch, "

[Bob Brown]

That was 25 thousands minimum wall thickness, not at 9 inches from the breech. I wasn't trying to say that that 25 thousands was safe at 9 inches. The 25 thousands minimum wall thickness was what he told me as well 7 or 8 years ago.

[Phillip Carr]

Per Griffin and Howe:

16. Barrel Wall Thickness - The thickness of the walls of a shotgun barrel. It is reasonable to assume that guns built by responsible manufacturers are safe to shoot, when new, with the loads for which they were intended. As the decades go by, however, as barrels are or buffed for rebluing and as occasional pits are honed out of the bores, steel is gradually removed from the barrels. The barrel walls, already built thin for lightness, become thinner still. At some point they become too thin for safety. It is important to know the barrel wall thickness of an old, well-used shotgun before shooting it. A rule of thumb states that the minimum barrel wall thickness should be .020" in a 12 gauge gun.

[edgarspencer]

I get the shakes each time I recall an 'over-restored' gun which measured .013" just at the end or the fore end. Several PGCA members were looking over my shoulder when I measured it. We had just walked across the parking lot at a certain venue in Southern New England.

[Rick Losey]

Yes

When we talk minimum wall thickness we tend to concentrate on the what of the measurement, when the where it occurs is a critical factor

[Dean Romig]

The more critical section of the barrel is the first 10" - 12" from the breech. Forward of that area pressures have dropped off radically and barrel wall thickness, though important, is far less critical. Though I would not shoot a gun with wall thickness of .013" I wouldn't hesitate to shoot a gun with less than the currently "approved" .025" - say, down to as thin as .020" or even .018" or .019" IF the chokes are Mod or less and more importantly, IF they are not pitted and IF they have never been honed and IF they have not been refinished in any way - in other words, IF they left the factory EXACTLY as they are today. (Extremely difficult to determine in a gun that has been heavily used)
Some guns were made as light upland guns and as such, the barrels were struck to what the factory considered to be safe to shoot with factory specified loads.

.... but that's just me - not suggesting anyone else do the same.





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[Drew Hause]

Lots of information here
https://docs.google.com/document/d/1ZIo0y746UsSRZIgRuuxwAbZjSBHitO_EanvwLYc-kGA/edit

and http://parkerguns.org/pages/faq/BarrelThickness.htm
NOTE: the image on the FAQ is NOT wall thickness recommendations; it is the dimensions used for the barrels evaluated by the Birmingham Proof House Trial. There was no chamber cut.
Scroll down a bit here
https://docs.google.com/document/d/1dnRLZgcuHfx7uFOHvHCUGnGFiLiset-DTTEK8OtPYVA/edit

I would observe that doublegun dealers now commonly run a wall thickness gauge down one side of a barrel and pronounce the barrel as "fine with a MWT of .030". As said, that number alone is meaningless and if a dealer, or the smith evaluating the barrels, can't provide the minimal wall thickness after measuring top, bottom and side (because of eccentricity) of the end of the chamber, the forcing cone, every inch to 9" from breech, and 9" from the muzzle, and MWT and where, a second opinion is mandatory.

BTW: I will have a table near the Parker tables at the Vegas show, and will have my bore gauge and wall thickness gauge to provide barrel evaluations, for a fee to offset the $375 table cost. I'll post a reminder as we get closer to the show, and I'm looking forward to meeting more of my "imaginary internet friends" in person :)

[Drew Hause]

Cross posted from another thread

How to use the Hosford gauge

Part 1
https://www.youtube.com/watch?v=1jQZn4kohH4

Part 2
https://www.youtube.com/watch?v=sfBP7a0TbjM


Henry gauge. The short metal piece is .038" to confirm the gauge.

http://pic20.picturetrail.com:80/VOL1373/6511424/24519472/406674912.jpg

http://pic20.picturetrail.com:80/VOL1373/6511424/24519472/412962360.jpg

The barrels are secured to a weighted box with bungie cords

http://pic20.picturetrail.com:80/VOL1373/6511424/24519472/412962359.jpg

I affixed a tape measure so the rule is not needed

http://pic20.picturetrail.com:80/VOL1373/6511424/24519472/409666365.jpg

[Jon Hancock]

That's a pretty neat tool. Sorry gentlemen, didn't realize so many have posted on this thread. You all have been most helpful.

[Craig Larter]

I use the Galazan wall thickness gauge. I find it easy to use. It would be interesting to compare wall measurements on a set of barrels using the Hosford gauge and the Galazan gauge.