Montana Title 45. Crimes § 45-8-307. Exceptions

(1) the manufacture of machine guns for and sale of machine guns to the military forces or the peace officers of the United States or of any political subdivision of the United States or transportation required for that purpose;

(2) the possession of a machine gun for a scientific purpose or the possession of a machine gun not usable as a weapon and possessed as a curiosity, ornament, or keepsake;

(3) the possession of a machine gun for a purpose manifestly not aggressive or offensive.