Just a reminder gentlemen. All gun barrel steels are not equal; in neither yield nor tensile strength. One barrel might tolerate bulge repair; another may not.
Tensile Strength
Pattern Welded steel 55,000 psi
Cold Rolled Decarbonized Steel & AISI 1018 Low Carbon (Mild) Steel 65,000 psi
1890s to c. 1920s fluid steel (Krupp, Siemens-Martin, Cockerill) 85,000 to 90,000 psi
AISI 4140 Chrome-Molybdenum Steel, Winchester Nickel Steel, Marlin Special Smokeless Steel, Remington Ordnance Steel, Bohler Blitz - 95,000 to 110,000 psi
Winchester Proof Steel (Chrome Moly 4340 or 4130) developed for the Model 21 and introduced in 1931 - 120,000 psi
Bohler Antinit Rostfrei Laufstahl chrome-molybdenum-vanadium 140,000 psi
And remember: Tensile strength is only a part of the equation for estimating bursting pressure. If the barrel is made of steel with a 60,000 psi tensile strength, that does NOT mean that it will withstand a shell with a 10,000 psi by a factor of 6.
Barlow's Bursting Formula P = 2 x S x 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.
Barlows refers to a thick wall pressure vessel (wall thickness greater than 1/10 1/20 ID); ie. a pipe capped at both ends with a static pressure.
Shotgun barrels are not designed to be pressure vessels as one end is open.
https://docs.google.com/document/d/1dnRLZgcuHfx7uFOHvHCUGnGFiLiset-DTTEK8OtPYVA/edit 
