The M-2 is a machine gun. In theory it is legal with the proper permit to own a machine gun ... but per Knappen II p.275 [a guide book on NJ's asinine gun laws] in reality there is no way to obtain the necessary permit and even if you did obtain permit would only be good to two years.
NJ is the worst state in the Union regarding guns. Individual US cities may be as bad or worse, but this is the worst state. It's easier for a citizen of NYC to get a concealed carry permit than in NJ. NY State isn't bad, though, just NYC. I assume it's because knuckle-headed city dwellers and suburbanites dominate the State.