Help identifying Nikko cased instrument

[ghp95134]

So assuming it is naval related then. Any idea on how this would work to examine an artillery chamber? ...

火管室検査鏡
Fire Chamber Inspection Mirror
or, as Nick says in better technical terminology:
optical percussion primer chamber inspection (mirror)

Perhaps something similar to the inspection done on lenses as shown below? I got some hits for smaller-sized inspection mirrors for rifles. Hmmmmmmmmmmm

Image from here

I found a USN image showing the primer chamber area of the gun's breech .... it must have been used to inspect that area. Similar to bore sighting? I would guess the instrument mirrors (see what I did there!) the head mirror that doctors used to use -- a bright light would reflect off the mirror onto the target, and could be viewed through the peep-hole in the center of the mirror.


Guy