If you are in MA you need an LTC-A, or in the case of just rifle mags, an LTC-B, to possess any kind of "large capacity feeding device. "
The pre/post ban thing is covered under a completely separate law.
It's also worth noting that violating either is a felony, although the "LCAFD without a license" law is about 10000 times easier to bag someone on when it comes down to it, because the standard of evidence is pretty low.