Rick36:
NC for some years had a provision in the Weapons of Mass Destruction statute (NCGS 14-288.8) which made magazines holding 31 rounds or more illegal. This section was eliminated when the statute was rewritten around 1993.
So, as Minuteman419 said, unless the magazines are marked "Law Enforcement, Military, Export Use Only", or have a manufacturer's date stamp after the Assault Weapons Ban was enacted in 1994, you are perfectly legal in NC. "Pre-ban" magazines should have a date (if any) prior to 1994. Most mags manufactured prior to that date will have no date stamps at all.
You should inspect all the mags you buy to ensure that you are not getting mags which could conceivably create a legal problem for you later. There have been threads on this site saying that some members have bought from some less-than-reputable dealers who sold LEO-only mags to them. In a worst-case scenario, if you should have to use the rifle in self-defense, and the investigating officers found you in possession of a banned magazine, a call to ATF could land you in a lot of hot water even if the shooting was justified.
Good luck with your new obsession.....