S.C. Code § 23-31-320
The provisions of this article shall not apply to the Army, Navy, or Air Force of the United States, the National Guard, and organizations authorized by law to purchase or receive machine guns, military firearms, or sawed-off shotguns or sawed-off rifles, from the United States or from this State and the members of such organizations. Any peace officer of the State or of any county or other political subdivision thereof, state constable, member of the highway patrol, railway policeman or warden, superintendent, head keeper or deputy of any state prison, penitentiary, workhouse, county jail, city jail, or other institution for the detention of persons convicted or accused of crime or held as witnesses in criminal cases or person on duty in the postal service of the United States or any common carrier while transporting direct to any police department, military, or naval organization or person authorized by law to possess or use a machine gun, or sawed-off shotgun or sawed-off rifle, may possess machine guns, or sawed-off shotguns or sawed-off rifles, when required in the performance of their duties. Nor shall the provisions hereof be construed to apply to machine guns, or sawed-off shotguns or sawed-off rifles, kept for display as relics and which are rendered harmless and not usable.
The provisions of this article shall not apply to any manufacturer of machine guns or military firearms licensed pursuant to the provisions of 18 U. S. C. Section 921 et seq., nor to any common or contract carrier transporting or shipping any machine guns or military firearms to or from such manufacturer if the transportation or shipment is not prohibited by federal law. Any such manufacturer shall furnish to the South Carolina Law Enforcement Division the serial numbers of all machine guns or military firearms manufactured by it within thirty days of such manufacture and shall be subject to the penalties provided in Section 23-31-340 for noncompliance.
S.C. Code § 23-31-320