These bullets were made to hide their carbide rear end inside the cartridge. They were designed to be given to the Afghans during the Soviet invasion to create barrel obstructions in enemy rifles.
Heard about them from this video (6:34). There doesn’t seem to be much in terms of English language sources, from my brief searching, so if anyone finds more info please share.
The video had mentioned they were weighted to be the same weight as normal cartridges but that last picture is a really good visual of that. The fact they didn’t have a way of telling by marking seems concerning.
If I remember right there was an issue with the Soviets (or maybe Russians at that point) ordering non corrosive ammo so their soldiers had to clean their guns less but they were identical to the corrosive ammo. So they still had to clean them all the time as they couldn’t ever be sure.
It always be like that. You just never know if this round will blow up your barrel, leave no dirt or just be normal.