In Colorado, you must obtain a valid NFA stamp in order to lawfully possess: A machine gun; A silencer (suppressor); A shotgun with a barrel(s) of less than 18 inches long; A rifle having a barrel(s) of less than 16 inches long; A weapon made from a shotgun if such weapon as modified has an overall length of less than 26 inches or a barrel(s) of less than 18 inches long; A weapon made from a rifle if such weapon as modified has an overall length of less than 26 inches or a barrel(s) of less than 16 inches long; Any other weapon, as defined in 26 U.S.C. 5845 subsection (e); and A destructive device.