Following World War II, this splicing technique had been lost. Japanese craftsmen in the latter part of the 20th century had no idea how this splice was installed.
In 1983, the joint was X-rayed. The joint was reverse-engineered, and Japanese craftsmen (and eventually Western craftsmen like Chris Hall*) learned to make it again.
Crazy Japanese Technique for Splicing the Bottom of a Rotted Column
A lot of the discussion I found online in reference to the photo speculated that that it was an Under/Over design. The video clearly shows it to be a SXS configuration. For the period both orientations were made.
Swivel guns where the barrels assembly could be rotated allowing the use on only one lock were also made. AFAIK swivel guns where only made as O/U guns.
Jeremiah Johnson just came on and noticed this very interesting muzzle loader.
Wonder who made it.
You get a better look in this video.
It's definitely a SXS.
Be sure to watch the tolerances on any case gauge you buy. I bought a L.E. Wilson several years ago when I decided to add 44 WCF to my inventory so I could shoot WB.
First batch of ammo I loaded worked no problem. As I only occasionally shoot WB the first 1K rounds lasted a while. Then I picked up a pair SAA and a pair of OMV in 44-40. So I started shooting 44 WCF at monthly matches.
Needed more ammo so I slugged the throats and barrels and everything measured out to .429. So I ordered bullets sized to .430. This where the problems started. Ammo would pass my case gauge but wouldn't chamber in my pistols. A friend had a finish reamer custom made specifically for my problem so we reamed the chambers and this fixed the problem for most but not all the ammo issues. More research showed that some of the bullets I bought were not properly sized and were .4305 to .4307 in diameter. Ran all the bullets through a .430 sizing die and loaded some more ammo. Again it all passes the case gauge but not all of it will chamber in my revolvers. Bought a Lee FCD die and ran all the loaded ammo through it and this has fixed 99% of the ammo.
Long story short I discovered that the part of the case gauge that is supposed to measure the neck of the case is WAY out of spec. It is cut to 44 Rem Mag dimensions. 🤬 🤬 🤬 🤬 Being as I have had this gauge for several years returning it is not an option. When I get ready to load 44-WCF again I'll invest in another case gauge and verify it is actually correctly made before I start using it.