SkeetTx & Grouse Guy,

I took the pictures of the Japanese single barrel to a Japanese gun dealer. Here is what he said:

Also the single barrel shotgun you asked about is an SKB.
The Kanji (Japanese) written is the company name and personal name of Mr. Sakaba Munenari. He manufactured the guns from 1833 to 1911. Please note that SKB means--- Sakaba - name of person and SKB letter in it.

I will try to get an exact interprestation of the Japanese lettering on the barrels.

Sincerely,
Patrick