Here we go again.
The metallurgical test results for this one barrel section will tell us a lot about the composition of this barrel, and other barrels that were made from the same heat of steel.
These results CANNOT be relied upon to accurately tell us the composition of any other Winchester Nickel Steel barrels.
Another Model 12 barrel, of identical wall thickness, using an identical load, made from a different heat of steel, may have reacted somewhat differently to an exactly identical obstruction. This is why, when hydrotesting ((Burst strength pressure testing) is done by tube mills, the test is done on each and every tube in that heat or order. There can be variability and defects causing hydrotesting failure even within the same heat. The tubes that pass testing are sold to the customer. The ones that fail are scrapped and re-melted.
Lloyd, you are correct about your understanding of elastic limit. That limit is clearly exceeded when an obstruction such as a wad, mud, or snow causes a bulge or burst. Even a low pressure load can cause such damage when contained or obstructed by something in the barrel.
A similar thing happens with bolts and screws made of steel. And this is the main reason for torque specifications. The term often used for threaded fasteners is yield strength. Over-tightening a bolt may seem like a great idea to really hold something, but you could actually weaken it and cause it to unexpectedly break if that yield strength has been exceeded during tightening. The threads have stretched. Once that limit has been exceeded, the damage is permanent.
A repaired barrel bulge will always be somewhat weaker than the surrounding un-stretched steel. That usually doesn't matter under normal circumstances, particularly if the bulge was out further where pressures are much lower. But if the condition that caused the bulge is repeated, the subsequent damage is more likely to be worse, at the previously bulged spot.
