Russians were masters of adopting ammo and firearms in weird dimensions and calibers that no one else can use. In case some other hostile army captured ammo and turned against them. Here some examples.
7.62x38r can not be shot in anything else but m1895, however if need be 7.5 Swedish/Swiss, even 8mm French can be fired from 7.62 nagant. But not the other way around.
Same with 9mm and 9x18 mak.
7,62x54 and x53 is the same ammo just as 7.63x25 and 7.62x25
One story I heard is that Soviet partizans were in need of 7,62x54, however during fighting all they had captured from Germans is lots of 8mm.
So in the contact with stavka they were sent by parachute a press that would by just simple whack of the hammer transform 8mm in to 7.62x54R