ORS 166.272: Unlawful possession of machine guns, certain short-barreled firearms and firearms silencers.

(1) A person commits the crime of unlawful possession of a machine gun, short-barreled rifle, short-barreled shotgun or firearms silencer if the person knowingly possesses any machine gun, short-barreled rifle, short-barreled shotgun or firearms silencer.

      (2) Unlawful possession of a machine gun, short-barreled rifle, short-barreled shotgun or firearms silencer is a Class B felony.

      (3) A peace officer may not arrest or charge a person for violating subsection (1) of this section if the person has in the person’s immediate possession documentation showing that the machine gun, short-barreled rifle, short-barreled shotgun or firearms silencer is registered as required under federal law.

      (4) It is an affirmative defense to a charge of violating subsection (1) of this section that the machine gun, short-barreled rifle, short-barreled shotgun or firearms silencer was registered as required under federal law.