We'll hopefully know a lot more when the barrels arrive.
To be clear, the wedge shaped top rib extension and hook are brazed to the barrels. See the images on p. 1. The joined metals have a very strong bond ie. a mono-metal, and the top wedge and bottom wedge should be considered as contributing to the barrel wall strength.
METL charges about $1000 for a formal Failure Analysis. Sectioning of the barrel and examination with photomicroscopy alone could be performed.
When discussing barrels alone, properly designed and manufactured barrels, of the correct steel for the application, free of defects or corrosion, used with loads for which they were designed and proved (by the maker in the U.S.), have an indefinite lifetime. Unfortunately, bad things happen to barrels in 110 years of use, abuse, and inexpert barrelsmithing.
The hang tag that came on that gun listed 2 1/2 dram 1 oz. shot, and Nitro powder loads then had similar pressures as today. And again, this is in reference to the barrels, not the wood or internal parts which do indeed wear, and wear out.
