Deltaboy, I too have great respect for LC Smiths. My main point was/is that I see no signs of an obstruction having caused your bbl split.
The vintage barrel materials project now underway will be analyzing another bbl, with a very similar and similarly-long split. Coincidentally, it also is from an LCS. It hasn't been analyzed yet, but certainly will be.
What caused that failure, or yours? I don't know yet, but can identify several possibilities.
Flaws do happen, even in the best products, and have a number of origins. Slag inclusions and voids were common in vintage steels. Homogeneous ("fluid") steel barrels were made several ways. Some of these drew the metal out considerably, in the longitudinal direction. This provided grain orientation and also tended to elongate inclusions and/or voids. Proof testing found the worst ones, but some undoubtedly survived proof.
Another possible cause or contributor is wall thickness insufficient for the local gas pressure. Locally-thin walls can be due to excessive striking (filing) on the outside, or boring out inside. Either can be done after the gun leaves the factory, to whatever brand and quality of gun. Of course, any local strength issue is exascerbated, increasingly, as local gas pressure is increased if higher-pressure loads are used.
One other common problem is a stress concentrator, which has a local weakening effect similar to a "flaw's." One good example illustrating this (or actually illustrating avoiding it), on well-made guns, is the rounding of the inside corner at the junction of the water table and standing breech. A square corner would suffer much higher stress for the same applied forces, than does a corner having an effective radius.
A longitudinal groove in a barrel wall multiplies the otherwise-uniform hoop stress, at its location. The exact effect depends on the geometry of the groove, the material hardness / lack of ductility. The perfect example is the effect created by a glass cutter. If memory serves, such a scratch in glass can raise bending stress by a factor of several hundred, at its location.
Engineers didn't understand until the 1930s that cyclic stress above a threshold value, but far below the yield point causes cumulative damage. This problem is magnified, often greatly, by seemingly-innocuous ornamentation that causes dangerous stress concentration. In one case photo-documented in a classic fatigue study, text stamped in a flat-bottomed font, closely-spaced, created high local stress that caused an airplane propeller to break with fatal results. (I don't have a photo posting site, but will be happy to forward a copy of this failure if anyone wants to post it.)
