what is this 40mm shell

[pzgr40]

Today I bought this very interesting 40mm shell. It has four longitudal channels that have radial holes in the longitudal direction connected to each channel. Also, the little holes connecting the fuze hole to the radail holes is at a different height. I have the idea that it's some kind of flash bang grenade, but that's a guess only. Who can tell me more.
Thanks in advance, regards, DJH

 

[pzgr40/42]

Would smoke / incendiary be an option? Somehow that sheet cap looks like it is supposed to "pop off".

 

[highlandotter]

my guess is short range incendiary. Propelling charge looks sort of small for weight of projectile.