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Minimum Wall Thickness at Point of Proof
Old 11-15-2016, 11:38 PM   #1
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Jon Hancock
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Default Minimum Wall Thickness at Point of Proof

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.
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Old 11-15-2016, 11:43 PM   #2
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Never mind. Found a good thread on this already.
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Old 11-16-2016, 08:43 AM   #3
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Please share the thread here so others can read it.

Thanks, Dean
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Old 11-16-2016, 09:53 AM   #4
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Quote:
Originally Posted by Jon Hancock View Post
at point of proof? .


just curious - What do you mean by that?

a distance from the breech?
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Old 11-16-2016, 01:24 PM   #5
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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?
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Old 11-16-2016, 03:24 PM   #6
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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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Old 11-16-2016, 09:23 PM   #7
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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.
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Old 11-16-2016, 10:04 PM   #8
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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

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, "
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Old 11-16-2016, 10:07 PM   #9
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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.
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Old 11-16-2016, 11:47 PM   #10
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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.
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