Id 25mm inert

[MINENAZ16]

Hello,
I'm trying to ID this round, inert, made of aluminium.
No marking.
First I thought to a drill round but very complicated shape (!).
Could it be a test cartridge (inspection tool) for 25mm gun or something unfinished ?
Max diameter of top : 25mm
Complete length of round : 235mm

 

[tomsk]

Looks like something someone knocked up on a lathe too much time on their hands but av been wrong before