In rating steel strength two very important factors are elastic limit & ultimate limit. The elastic limit is the point at which if exceeded it will stretch but not return to normal. The ultimate limit is the point at which it will actually rupture.
As applied to gun barrels a barrel with a bulge means the pressure exceeded the elastic limit but not the ultimate. If it bursts, both were exceeded. Iron & mild steel has a low elastic limit in relation to its ultimate. As steel is alloyed & heat treated etc both limits are raised, but in most cases the elastic actually goes up higher in proportion than does the ultimate, thus the gap between the two narrows.
With modern steels such as 4140 etc the limits are quite high. It would normally take something of a catastrophic nature to exceed either, consequently it is more common to see one of these burst rather than bulged, but a bulge can also occur in them as well.
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 the phenomenon of loading too slow a powder to too low a pressure by someone thinking they would be doing it a favor. Powders should be kept within the pressure range for which they were designed. Any gun which will not take lite loads for the gauge at pressures in the 7.5K-8K should be permanently hung on the wall & not be allowed to be fired by anyone.
Most likely if this gun had been shot with "Factory" loads not exceeding 1oz @ 1200 fps regardless of their pressure it would still be usable.
Understand I do reload for my Damascus barreled guns. I keep the pressures at around 8K with the fastest burning powders that will stay within this pressure range. "SLOW" burn powder were designed for Heavy payloads & High Velocities without exceeding SAAMI pressures, not for low pressures.
My thinking is that a lot of people need to learn this. I learned it through some squib loads which fortunately did not bulge or burst the barrels, but I now realise I was skirting with danger.
In fact when I learned it I was shooting with a new set of Bohler Steel barrels on an old Lefever. Had I had the original Damascus barrels on that day results may well have been different.
