Danke Kuduae!

What you say about calibers makes sense.

But still, the x53R case designation is not that clear (not that it makes much of a difference, either). The russians have always designated their old military ammo 7,62x54R while we Finns used 7,62x53R for what is essentially an identical cartridge. I know that many claim that there actually should be a 0,5 mm difference in case lenght, but in reality it often is not there. That's why I wondered why they chose the x53R for a civilian round.

@Lancaster, what is the actual case length?