Hope that this helps
Under Massachusetts law, a “large capacity feeding device” is defined as “(i) a fixed or detachable magazine, box, drum, feed strip or similar device capable of accepting, or that can be readily converted to accept, more than ten rounds of ammunition or more than five shotgun shells; or (ii) a large capacity ammunition feeding device as defined in the federal Public Safety and Recreational Firearms Use Protection Act, 18 U.S.C. § 921(a)(31)." Mass. Gen. Laws ch. 140, § 121. This does not include “an attached tubular device designed to accept, and capable of operating only with, .22 caliber ammunition.” Id.
The sale, offering for sale, transfer or possession of large capacity feeding devices for assault weapons (as defined under Ch. 140, § 121), is prohibited unless such device was lawfully possessed on September 13, 1994. Ch. 140, § 131M.
Large capacity feeding devices designed for large capacity rifles and shotguns may be lawfully possessed by a holder of a Class A or B license to carry. Ch. 140, § 131(m). Large capacity feeding devices designed for handguns, rifles and shotguns may be possessed by holders of a Class A license to carry only. Ch. 140, § 131(a).
Ever since the Gun Control Act of 1998 became law, license to carry applicants are faced with increased scrutiny, even if they have had a license for decades. In many communities it is very difficult to get a license to carry, particularly if you want a Class A license.