Arisaka No Mum. Anybody got a clue?

[Bagman]

I even have the wooden box that the ship's carpenter made for him to ship it home.

 

[Yotarockcrawler]

😳Priceless!

 

[enfieldguy]

Very possible this one ended up in China after the war. I've seen several examples where the mum was completely erased once the Chinese got hold of them.
You generally see two types of mum defacing...fully or semi ground, or the mum is lined out.