The Hoop Stress in a thin-walled cylndrical pressure vessel, i.e. this shotgun barrel, is given by:
Hoop Stress = (Radius / Wall Thickness ) times Internal Pressure
Assuming a Nominal Pressure at 9 inches from the breech of 5,000 psi (Only actual measured data would tell us what it really is), we can estimate the Hoop Stress in this barrel.
Estimated Hoop Stress = (0.331 / 0.018) 5,000 = 92,000 psi
Lacking firm data on barrel steel strength and fatigue properties, Yield and Ultimate Strength, Endurance Limit, Fracture Toughness, possible pre-existing internal flaws, etc., I would certainly not be willing to fire it, especially on a regularly repeated basis, at anywhere near this stress level.
Just because it did not burst during several hundred rounds so far, does not mean that it will not burst on the next one, or many thousands of rounds later. Fatigue failures in steel can occur after up to more than a million cycles of loading, with the load necessary to cause failure going down progressively as the number of loading cycles increases. They are typically sudden, complete, and sometimes catastrophic.
Last edited by vangulil; 09/21/11 09:25 PM.