I believe that the 30-30 was listed as the 7.62X51r because the Mosin cartridge was variously known as the 7.62x4r, 53r and sometimes even 52r. I have seen Finnish and Slavic sites referring to it as such, even while listing another length as a standard cartridge for issue rifles. On the other hand, Municon lists the 30-30 as both the 7.62x51r and 52r. Various French and German sites list the 30-30 as the 7.62x52r when used in drillings or combination rifles.