well, you are really only dealing with military rifles then.
See, rifles are like pizza, you can have any toppings on them that you want. In the same way, a rifle maker designs a gun, and then has it available in a wide variety of calibers.
The only real exception to this is the military, they get a rifle (probably the same one the manufacturer would willingly chamber in a whole bunch of different cartridges) and then they specify that they want it all in XYZ chambering.
The 'Official' russian cartridge from the close of the 19th century to a bit after WW2 was the 7.62x54R, pretty much every gun they had used that cartridge (with the exception of some of their more experimental semi-auto types) they then progreesed to 7.62x39 then 5.45x39
The best bet for you is to pick up some refrence book on military arms, as you page through it, you will see the same country using the same loading again and again and again, then replacing it and usign that one over and over and over.
Right now, it's more than just one country-one catridge, whole blocks of countries based on mutual defense treaties all use the same cartridge in a wide variety of rifles.
In WWII, the brits had the 303, the americans had the 30-06, and the russians had the 7.62x54R, all of which are very very similiar ballistically...but they don't all fit in the same gun.
We smartened up, and after WWII we and the brits and the auzzies and a few others all decided we need the same ammo, and eventually decidied on the 7.62x51, or 7.62 NATO. Now, the Americans used the M-14, the auzzies and the brits had FN-FALs, others went with the G-3 as it was a bit cheaper, etc etc. Each country used the gun they liked best, just made sure it shot 7.62 NATO
Then we switched to 5.56 NATO. The Americans chose the M16 to shoot that round, the brits chose the L85, the swiss went with the Sig550, the Israelis went with the Galil (a modified AK really) etc etc