This ammunition is the 7.62 X 54mmR surplus ammo out of Bulgaria. You can usually get this in 440 round tins or 880 round crates (two 440 tins in a wooden box). This ammunition is corrosive to your gun but that is not all that bad! Basically, all you need to be aware of is that when you are done shooting with this ammo you need to clean your gun with soap and water. You really just need to run a couple of patches up and down the inside of the barrel that have soapy water on them. This will counter-act the chemical that makes these rounds corrosive. So, no, cleaning your gun with regular gun oil afterwards will not counter-act the corrosive ingredient. It must be soapy water. Some people say you can use Windex but that is a rumor I have heard. Then you just clean your gun with gun oil like you normally would.
This ammo is mainly used for the Mosin-Nagant rifles.
Update: I haven’t seen the Bulgarian stuff in a while, but you can pick up some Romanian made 7.62x54r surplus ammo at Sportsman’s Guide.