Pressure loads

[edgarspencer]

Perhaps shot-shell manufacturers should refer to their 'low' pressure ammo as ' lower' pressure, but they (and I) probably don't need to know what pressure is necessary to blow up a barrel. It's easy enough to know the range of pressures being offed, and if their's falls on the lower end of the scale, that's all that necessary to legitimately call them low pressure.
Lots of tests have been run on various steels used to make barrels by Parker Brothers. These tests, undertaken by members, and using labs and procedures considered meeting standards such as ANSI, ASTM, ASME, and NAVSEA, were published both here, and in Parker Pages articles.
Alloy steels, typically CrMo, and CrNiMo, have UTS (Ultimate Tensile Strength) above 80,000 psi, and most are in the 90-60 range (90,000 UTS, and 60,000 Yield strength) not,"Shear Strength" as stated above.

I don't think anyone has ever done extensive testing on composite barrels like that done on steel barrels. In order to do a proper test, samples would be examined both non destructively and destructively. It's pretty hard to say what is "specification" as you're dealing with at least two distinct materials, and in a form which would be difficult to segregate. These materials aren't homogeneous but from a practical standpoint, have to be treated like they are, knowing any test results are pretty random.

[Michael rivers]

Ok great thanks I just need numbers to refer to.

[Drew Hause]

Michael: this is important
Tensile strength is only a part of the equation for estimating bursting pressure. If the barrel is made of Twist with a 50,000 psi tensile strength, that does NOT mean that it will withstand a 10,000 psi load by a factor of 5.

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 refers to a pipe capped at both ends with a static pressure (a pressure cylinder) so does not work well for unobstructed shotgun barrels; which are not designed to be pressure vessels as one end is open and the pressure rises and falls quickly.

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

BTW: Wallace H. Coxe, in "Smokeless Shotgun Powders: Their Development, Composition and Ballistic Characteristics" published by E.I. du Pont de Nemours & Co. in 1931 cites 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 only 5,600 psi.