http://www.eugene-or.gov/DocumentCenter/View/2693This only applies to Eugene. For a complete understanding, you must know the Lane County Laws and State Laws.
http://www.youtube.com/watch?v=v7UMdniHWkIMy understanding is Open carry is legal, but if you are packing around a rifle they might ask you to comply with a disturbance ordinance seeing as how it would be dickish to publicly scare people that don't understand the law. Mainly OC seems to be understood as a pistol-carry law for Eugene and not a rifle. And Springfield is not open carry.
Also, Even though Eugene is OC, YOU CANNOT CONCEAL ANY AIRSOFT RIFLE NOR HAVE IT WITHIN REACH IN A VEHICLE. Pretty much if you get pulled over, you must tell the officer right away that this is whats in my vehicle and must be visible to the public; not buried or underneath the seat. The orange tip is not required.
If you look to be younger than 18, they can ask for ID and you must comply. If you are packing a pistol and you don't look 21, they will require ID and the registration of the firearm.
Obviously, if you "brandish" a airsoft rifle or pistol, you can be fined and placed under arrest. Unless you are trying to save the day with it....
Again, Each locality is different with ordinances as well as the city limits. Lane County has it's own and is much different and follows closer to State and Federal laws.