i shoot :
-brown case Norinco non-corrosive , pretty good
-South? African brass cased berdan, unburnt powder
-BXN CZech grey casing, got more kick than normal, dirty.
those are all 7.62X39.
people usually say that soviet ammo is the dirtiest, but if you clean your gun you can shoot anything.
dont know about 7.62X25, thats for tokarev pistol i think?