Not legal to possess the 30 rnd mag in NJ...body is considered the mag I believe so pulling the guts out doesn't save you. Have you looked for the pmag 15/30s or 10/20s, they are 10 or 15 rounders built from a 20 or 30 round body. About $30 if you can find them but they shouldn't be as hard to find as the 20 and 30 rounders, nobody is looking to hoard 10 or 15 round mag.
"The whole of the Bill (of Rights) is a declaration of the right of the people at large or considered as individuals.... It establishes some rights of the individual as unalienable and which consequently, no majority has a right to deprive them of." (Albert Gallatin of the New York Historical Society, October 7, 1789)
"A free people ought not only to be armed and disciplined, but they should have sufficient arms and ammunition to maintain a status of independence from any who might attempt to abuse them, which would include their own government." - George Washington