I have been studying the construction techniques of Japanese bladesmiths, I call this stile of a soft steel jacket over a hard steel core "hot dog in a bun" because that's what the preform billet looks like . This method is common in Norway and Scandinavia also for pukko knives, however I was told by a smith from Norway they use angle iron for the jacket in modern times lol. I tried it for the first time yesterday, and succeeded so, since "this thread is useless without pictures" I thought I'd do one better and make a video. Thought you guys over here in the custom knives section might be interested to see it too.
I managed to capture everything but forging the blade out before the memory ran out, but the major parts are in there, I hope it's clear but if anyone has any questions feel free.
and here's the knife I ended up with, I forged it by hand a bit after the video, then cleaned it up on the grinder.