20mm M55A2 shortened ID

[MINENAZ16]

Sometimes we find this strange short 20mm in France.
Inert, plugged, no tracer.
Markings on the body are 20MM-M55A2-7-MIY-78
First time I thought to a modified US practice 20mm M55A2 but I saw this short round three different times.

 

[kiwieod]

i think yugoslavia also produced 20mm M55 series ammunition