....The fact that this barrel bulged rather than burst simply means for whatever reason the pressure exceed the elastic limit, but not the ultimate. This does not mean it was of superior metal, but rather more likely it was of rather soft metal with a rather low elastic limit.
While freely admitting for it to have occurred in Both Barrels is at best highly unusual I still say it has all the appearance of a localized obstructional bulge. May well have been brought on by....
Shotgunjones mentioned these were good tubes, and I agree. I think you summed what might be going on. While it may(?) not be their fault, the barrels did fail. I believe all gun barrel steels are considered 'soft'. The lucky thing was that it failed slowly, and signs showed that it was probably closer to it's ultimate limit than before the bulges.
The problem with being good tubes is the commentary is completely ignoring the thickness of the tubes. What's the point of having a barrel thickness gauge if the only requirement is to check barrels for obstructions and being alert to signs that an obstruction might have occurred, such as a squib load.
I think the British proof houses are plenty evidence that good tubes going in to the test, don't always come out the other end as good tubes. The point being that if obstructions aren't part of the test, then 'relatively', I think obscene, low over pressures can damage gun barrels.
If it were my money buying a gun with 'original' barrel and bore specs, I think I'd expect the barrel patina to nearly obscure the damascus pattern. Maybe, the bore would be a little frosty in likely places. Refinishing gun metal is supposed to remove 'negligible' amounts of metal, but I don't think that is always so.
If(?) no obstruction were present, then there seems to be little point to worrying about 'reasonable' over pressures. We seem to worry about over pressure when every thing is going well. Some metallurgists will say that the metal in the bulge is likely stronger now. Why not tap it down and call it good.
