The Alec Steele YouTube videos are interesting. I watched several of them a few years ago, and rewatched a few today. I think he misinterprets a number of things, such as the extent of probable diffusion of carbon into the iron ribbands during forge welding. He makes it seem as if the carbon levels between the iron and steel layers nearly equalizes, and that carbon atoms move deeply and easily into the iron. If that were true, there would likely be little to no contrast between the layers after blacking and etching. It seems more likely the actual extent of carbon diffusion from the mild carbon steel into the neighboring iron layer would be even less than we see during bone charcoal case hardening.
Another point that got my attention was when he said the chemise (French word for "shirt") was made out of tin. The chemise was a thin sacrificial layer between the mandrel and the ribbands being welded around the mandrel. It supposedly aided in removing the barrel from the mandrel bar after welding, and was bored out when the rough tubes were bored. Since the melting point of tin is a relatively low 450 degrees F, the red hot ribbands would quickly melt and solder the rough tube to the mandrel. I recall Pete Mikalajunas telling us that the chemise was made out of thin sheet iron, which makes much more sense.
What's really mind boggling is how this old technology that was used to produce many millions of rifle, shotgun, and handgun barrels in multiple countries was all but lost in such a short time period. We're fortunate that a few old photographs and films of the process survived. Not only that, it is evident that modern shops with up to date furnaces, forges, and hydraulic equipment still haven't been able to come anywhere close to replicating the best Damascus produced over a century ago. I'd guess that Alec Steel's first successful skelp welded tubes would be very lucky to survive 500 psi if subjected to hydro testing.
