Japanese Shrapnel piece

[flatlander]

I recently picked up this rather large piece of shrapnel from a WW2 US career officers estate. There were some WW2 Japanese shoulder boards, collar tabs etc so I am hoping this is Japanese also. Just wondering if anyone can ID this?
Thanks for looking.

[flatlander]

rev

[Gimpy117]

I dunno..considering the Japanese threw just about everything at our service men, bombs, planes, themselves....it could be anything

but I wanted to break the ice on this one.

[Don D.]

Looks like a piece from a mortor round to me.

[Alan Smith]

I think it is from an AP/HEprojectile, likely from a gun around 40mm or so. Near the base you can see the external groove where the brass rotating band was once in place. Also, on the inside you can see threads where it was internally fuzed at the base. If it is Japanese, I would guess it is from one of their 37mm guns.