NFA Firearms are highly regulated, but any person or entity allowed to purchase or own a common pistol can also purchase or own a NFA Firearm under Federal Law. South Carolina does not place any additional limitations on NFA Firearms properly owned and registered under the NFA.
A person of age (21 years) can buy a firearm, including a NFA Firearm, as long as certain disqualifying circumstances do not apply. Disqualifying circumstances include:
conviction of a crime punishable by more than a year in prison (regardless of how much time a person is actually sentenced to serve);
being a fugitive from justice;
addiction to or unlawful use of any controlled substance;
adjudication as a mental defective or having been committed to a mental institution;
being an illegal alien or unlawfully present in the US;
being an alien admitted to the US on a non-immigrant visa;
dishonorable discharge from the Armed Forces;
having renounced your US citizenship;
conviction of a crime of domestic violence; or
being subject to a court order, after due process, that restrains a person from threatening an intimate partner or related person and explicitly prohibits the use of force.
These disqualifying circumstances can be found in full in 18 U.S.C. § 922(g) and are the same restrictions that apply to purchasing any firearm. Practically speaking, if you pass a background check to buy a pistol, or you have a Concealed Weapons Permit, you can purchase a NFA Firearm in South Carolina. NFA Firearms are not subject to any special prohibitions on ownership.
If an individual owner of a NFA Firearm becomes disqualified, he or she must take action to immediately transfer the firearm out of his or her possession. This is problematic because the ATF is currently taking upwards of six months to complete Form 4 transfer requests. An individual can work around this by immediately taking the firearm to an authorized shop for repair, servicing, and maintenance while waiting for the transfer to take place, but this is a grey area of the law that is best avoided.
Trustees of a NFA Firearm Trust cannot include anyone who is disqualified from purchasing or owning a firearm. This is a simple restriction, but one that is ongoing. Should a current trustee suddenly become disqualified due to one of the above circumstances, it is the duty of the remaining trustees to remove him or her from the trust. This can be accomplished with a simple amendment by the settlor and a letter noting the change in trustees to all parties commonly dealing with the trust. Fortunately, this solution is simpler than when an individual becomes disqualified, and is much more straightforward.