Can you help me identify this Chinese or Japanese shell

[Shangguan]

Hello all. I was wondering if anyone out there could help me identify this bullet. It is made of cast iron and is hollow without any markings. The grooves appear to have been turned on a lathe. I purchased it in the North of China. I thought it might be steel, but when I cleaned off the rust and dirt, it turned out to be cast iron. Could the groove be for a brass sabot? Does anyone have any idea how old it might be?

It is 45cm in diameter, 8cm in length.

Thank you so much for any help you might be able to give me.

[Shangguan]

It turns out that this is the grenade head from a Japanese Type 98B Stick Grenade.

I am surprised nobody had anything to say here.