20mm projectile ID

[ThomasP]

FWIW

During WWII the British used pressed in tracer compound on a fair number of its smaller rounds (upto 6pdr at least, maybe larger), sealing the opening against moisture and such with a celluloid(cellulose?) disc. The Americans copied the method for most of their US/UK compatible ammunition of the same types.

 

[stuff]

Here is a loaded (inert) and unloaded example. Note the slight difference in length. When I purchased these they were described as plate test rounds.

 

[AKON_]

Here is a loaded (inert) and unloaded example. Note the slight difference in length. When I purchased these they were described as plate test rounds.

That's a step forward in identification. Can we see a photo of the bottom of the cartridge and the total length?
PS:I have today's coffee grounds here and it says Ho-5 (Japan) so I hope I didn't drink bad coffee
Akon