Japanese Brass cylinder with range charts engraved(not shell casing, not trench art)

[tusig1156]

Any ideas as to what this is? Its not a shell casing because the engravings seem too well done and it appears to have a use. This also makes me think this isn't trench art because its too well done. Its been made into a lamp but the grey part on top appears to have been part of the original part. The brass part can rotate but the grey part stays still. My best guess is some kind of chart put on a cylinder and mounted to some sort of gun/tank/ship to use in figuring elevation for some gun to fire at a certain range. If anyone can read japanese, that would probably answer a lot of questions.

 

[tusig1156]

 

[butterfly]

Sorry I cant identify it for you but I think you are right. It appears to me at least to be some kind of ranging drum (if thats the right word for it??) for use with sighting. The scale with 'diagonal' lines would possibly have been read through a window of some kind.
Its certainly an attractive piece and maybe someone will shed more light on it for you. Translation of the Japanese characters will possibly also shed more light.

I look forward, like yourself to finding out exactly what it is..... good luck.
Nice item thanks for sharing
regards Kev