“Innerstructure corrosion”. As a layman I can’t imagine a more insidious-sounding barrel affliction.

If it does exist in a set of barrels, there seems currently to be no way to check for it.

Barrel thickness gauging would be irrelevant to determine its presence, extent or the frangibility of the metal affected.

“Shiny”; “pitted”; “bulged”, “dented” and “scuffed” are all observable, manifest descriptions of metal surfaces. Conversely, “innerstructure corrosion” is inherently latent.

Drew H. has said elsewhere on this Forum that: “No standards exist for radiography of pattern welded barrels, and x-rays can not differentiate between defects within the barrel wall, and pits on the interior surface”.

And further, “It has been my hope that a NDT expert with access to testing facilities, and doublegun interest, might develop a pattern welded barrel evaluation service. To my knowledge that has not yet occurred”.

Are there any recorded mishaps that with reasonable assurance can be attributed to “innerstructure corrosion”?

Long answer, and the short version of "Zircon's" metallurgic study of the GH & VH barrels
https://docs.google.com/document/d/1...K7G9IBs4g/edit

Short answer

Welds can fail

http://pic20.picturetrail.com:80/VOL.../247636155.jpg

Properly fabricated pattern welded barrels do NOT develop "orange lace"; "interlaminar elecrolytic [sic] corrosion" nor embrittlement (crystallization)

Freshly cut twist and crolle damascus barrels

http://pic20.picturetrail.com:80/VOL.../409066906.jpg

Looooong answer
https://docs.google.com/document/d/1...hIiY62Hx4/edit

With the wads available back at the time your family Parker Bros. was made, the recommendation for these guns was to use over-size wads -- 9-gauge wads in 10-gauge guns and 11-gauge wads in 12-gauge guns. Note the loads No. 56 and 57 for Parker Bros. guns in this 1886-7 Chamberlin Cartridge Co. catalog --
Attachment 64310
Attachment 64311

These old Parker Bros. guns with their over-size bores have been used for the last hundred and twenty years or so with regular wads. Over-bore barrels have been in and out of fashion throughout the history of cartridge shotguns. Today we have a number of trap shooters banging away with Stan Baker "Big-Bore" barrels with .800-inch bores all the way to the choke?!?

Russ, do you mean 'Inter-granular Corrosion? This is a condition where attack takes place withing the grain boundaries. Generally associated with Austenitic stainlesses, and not unheard of in inadequately heat treated carbonsteel.
I can, as least conceptually, see where corrosive residue from primers and powder, will form acidic compounds given enough moisture. This would be much more serious in pattern welded barrels, less so in carbon steel barrels of reasonable metallurgy and sound heat treat practice.

There you go Edgar, wonder where you had been. I remember you using that proper "inter granular corrosion" term and definition last time we talked about fluid steel and it probably not being an issue. Welded, twist, Damascus etc. a little more opportunity in process and if not cared for properly for maybe an issue to arise. Nothing is risk free.

Oliver, beautiful family heirloom. I have an 1881 under lifter that I shoot occasionally with very light loads. It shoots just fine, breaks targets and drops birds with no problem. Take it out and enjoy your family gun!

If G&H said it was safe to shoot I would order a flat of 7/8 oz. loads from RST and go shooting. They are smokeless loads but the pressures will be low. Probably lower than many usual black powder loads. A lot of us shoot guns that old with RST loads. The photo of the blown up gun shows a gun blown up with a hot, modern, sporting clays competition load.

There is even a question or speculation that a least on one of the occasions mentioned where there was a cataclysmic failure there might have been an obstruction or even a double charge. Nothing is risk free though.

Probably the odds of being killed in a car crash driving to the range or going hunting are greater than a gun blowing up in your face if you take reasonable care.