An important but 9 year old thread revived by Bill, then his comment deleted.
I went through each page and unfortunately can not edit nor restore the images.
I'll address Bruce's question in the last post from 2014 then stick to wall thickness measurements
To clarify the issue of barrel strength and wall thickness, tensile strength is only a part of the equation for estimating bursting pressure. There are several burst formula.
All refer to a pipe capped at both ends with a static pressure (a pressure cylinder).
UNOBSTRUCTED shotgun barrels are not designed to be pressure vessels as one end is open and the pressure rises and falls quickly SO (according to several mechanical and metallurgical engineers with whom I spoke including Eldon) NONE OF THE FORMULA WORK.
Barlow's formula P=2 S t / D
P=Bursting pressure in psi.
S=Tensile strength of material in tube wall.
t=Wall thickness in inches.
D=Outside diameter in inches.
Burrard used the Alger Burst Formula
Burst pressure = Ultimate tensile strength x 3(OD – ID) / OD + 2xID
The Hoop Stress Formula doesn't reliably predict shotgun barrel failure either
Shotgun barrels are "thin wall cylinders"
σ = pr/t
p= pressure; r is the inside radius; t is the wall thickness
Bottom line is we can't estimate bursting pressure in a properly designed and fabricated barrel, free from internal or external defects.
We do know that it took Sherman Bell >30,000 psi to burst both Parker D3 Damascus and Vulcan Steel barrels
Here's a long thread from last year about measuring wall thickness which has lots of end-of-the-chamber numbers WHICH ARE MUCH MORE CRITICAL than MWT in the distal 1/3 of the barrel.
https://www.doublegunshop.com/forums...&Number=615160
More thoughts regarding barrel evaluation & load recommendations
https://docs.google.com/document/d/1...vwLYc-kGA/edit
We now have LOTS more data regarding the actual loads used in our vintage doubles, and Parker Bros. and the other maker's load recommendations. There are several pressure-distance curves also.
https://docs.google.com/document/d/1...aAfUOZEFU/edit
BTW Parker Bros. documented as early as 1893 that they proved barrels in-house.
A Parker Service and Proof Load table was published in the 1930s and reproduced in the
The Parker Story p. 515. 12g 2 3/4” shell Service Pressure is 10,500 psi. Definitive proof used 7.53 Drams Black Powder and 2 oz. shot with a pressure of 15,900 psi. The pressure was no doubt measured using LUP and modern transducer values would be
10-14% higher, or more than 17,500 psi.
LTC Calvin Goddard reported the same numbers in “Army Ordnance”, 1934. He wrote that Parker followed the SAAMI standards of that period: 13,700 psi proof, 9500 psi service for 2 5/8” chamber; 15,900 psi proof, 10,500 psi service for 2 3/4” chamber (by LUP)
+ 10-14% for modern transducer measurement.
Threaded Mode