I use 7.62x54r.net as a common reference for anything MN. This is what they have to say about the original round.

"Along with the Mosin Nagant rifle a new "small caliber" cartridge was adopted by Russia known as the Three Line (7.62mm) Rifle Cartridge, Model of the Year 1891. Later known as the 7.62x54R, it utilized the relatively new smokeless powder ignited by a Berdan primer to fire a 13,73 gram (212 grain) round nosed bullet at approximately 615 meters/second (2020 feet/second)."
http://7.62x54r.net/MosinID/MosinAmmoID.htm

Nora