From the Massachusetts laws;
http://www.mass.gov/legis/laws/mgl/140-131.htm
The first portion reads:
"CHAPTER 140. LICENSES
ARTICLE OF FIREARMS.
Chapter 140: Section 131 Licenses to carry firearms; Class A and B; conditions and restrictions
[ Text applicable as provided by 1998, 180, Sec. 80.]
Section 131. All licenses to carry firearms shall be designated Class A or Class B, and the issuance and possession of any such license shall be subject to the following conditions and restrictions:
(a) A Class A license shall entitle a holder thereof to purchase, rent, lease, borrow, possess and carry: (i) firearms, including large capacity firearms, and feeding devices and ammunition therefor, for all lawful purposes, subject to such restrictions relative to the possession, use or carrying of firearms as the licensing authority deems proper; and (ii) rifles and shotguns, including large capacity weapons, and feeding devices and ammunition therefor, for all lawful purposes; provided, however, that the licensing authority may impose such restrictions relative to the possession, use or carrying of large capacity rifles and shotguns as it deems proper. A violation of a restriction imposed by the licensing authority under the provisions of this paragraph shall be cause for suspension or revocation and shall, unless otherwise provided, be punished by a fine of not less than $1,000 nor more than $10,000; provided, however, that the provisions of section 10 of chapter 269 shall not apply to such violation."
A properly licensed indivual MAY possess large capacity feeding devices (AKA hi-cap mags, normal capacity magazines, etc.) with the proper license.
In answer to another statement, "sorry, I ment you cant buy them out of state" I know of no prohibition against buying a large capacity feeding device from out of state. Now some dealers may say that they cannot or will not ship them to Massachusetts but that is a different story.