Assuming you're referring to the Mosin-Nagant rifles, they were designed to use a 7.62x4 rimmed (7.62x4R) cartridge. The Finnish rifles are designed to function ideally with the heavy ball cartridges, while the Soviet (including ones made in France and the USA under contract) and Chinese rifles are optimal with light ball cartridges. A VERY limited number captured by Austria-Hungary during the First World War were rechambered for the 7.92x57 Mauser cartridge, but these are extremely rare, and if you have one with a production date of 1918 or later, I can guarantee you it won't be one of these.
7.62x54r just like every other mosin naganr
7.62 x 54R
7.62x54(R) rimmed rifle ammunition.
7.62x54R
With civiian ammo, it is the caliber. Military ammo- year made, and where
22 caliber ammo
the m16 uses 5.56 caliber ammo
Measure it, compare it to other known cartridges. Most military ammo is not marked wit the caliber/
No such caliber as .32 Special. Use the caliber of ammo marked on the gun.
A 22 caliber pistol holds a dose of 22 caliber ammo.
38 caliber revolver ammo
a "308" measures .308 inches while most 30 caliber ammo measures .312 inches. Strange as it may seem both are classifies as 30 caliber ammo.