When buying ammo, make sure it is 7.62x54R, a case about 2 1/8 inches long with a rim. Don't get 7.62x39, also a Russian round, but shorter and smaller.
Most of that ammo on the market is old surplus and is corrosive primed, so clean the barrel good after firing it.
Edited to add. If you fire that 18" barrel rifle, PLEASE use both ear plugs and muffs, plus shooting glasses; the muzzle blast will really rock!
Jim