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Unread 01-26-2015, 03:32 PM   #13
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Drew Hause
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Paul: Tensile strength is only a part of the equation for estimating bursting pressure. If the barrel is made of Decarbonized steel with a 60,000 psi tensile strength, that does NOT mean that it will withstand a 10,000 psi load by a factor of 6.

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.

Barlow’s, and the other formula (Alger, Boardman and Lame), refer to a pipe capped at both ends with a static pressure (a pressure cylinder). Shotgun barrels are not designed to be pressure vessels as one end is open and the pressure rises and falls quickly. I've discussed this issue with Eldon and a metallurgical engineer and there is no working formula for open end tubes.

Wallace H. Coxe, in "Smokeless Shotgun Powders: Their Development, Composition and Ballistic Characteristics" by E.I. du Pont de Nemours & Co. in 1931 published the following pressure/distance curve.



He also cited a study in which a fluid steel barrel was cut to 9” and capped, then a series of progressively increasing pressure loads fired. The barrel cap was blown off and barrel burst at 5,600 psi.

Comment in Sporting Guns and Gunpowders regarding the Proof House Report of 1891
http://books.google.com/books?id=inQCAAAAYAAJ&pg=PA16
"These experiments serve to show what a very large margin of strength there is in a good gun barrel, when ordinary charges are used. The (Damascus) barrels which gave way earliest under (the second phase destructive test) had withstood the strains of…about four times as great as the regulation proof; while the steel barrels (Siemens-Martin and English “Superior Barrel Steel”) were tested…with charges averaging nearly five times as much as the ordinary proof-charge.
Although the steel barrels showed the greater amount of endurance, the strength of the Damascus was so much in excess of all ordinary requirements that no fear need be felt of their giving way when the work is properly done."

Last edited by Drew Hause; 01-27-2015 at 06:03 PM..
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