7,62 x 39 curious ammo

[bucnball]

Have  found  a  square  blister  pack  of  10  rounds  that  says  10  stuck  (with  two horizontal dots in the top of the U) and M43 Ub in raised letters on the plastic blister. The blister pack is backed with paper . The bullets are round nosed and dark gray. A magnet confirms the bullets are sheathed or plated with steel . Any one know what they are or were designed for ? Thanks !

[Garufa]

East German “ubung” practice ammo.  Has a nylon core steel jacketed bullet.