21 85 cartridge Indentification request

My dad found this case on cementery one day. Im from Poland (podlasie).
Could you guys please indentify this cartridge?
I found informations that It could be factored in MESKO factory in 1985, is it true?
And what in what gun could it be used?

Correct. It seems to be a (soviet) Polish-made M43 cartridge case… cal 7.62x39.
Standard Avtomat Kalashnikova cartridge. Also SKS cartridge.

Merry Christmas
Doc AV

And Mesko is correctly identified of course.

In 1985 - PREDOM-MESKO :-)