Per Wikipedia:
High capacity magazines This page was last modified on 26 January 2012 at 20:28.
The term high capacity magazine is used to describe magazines that exceed a specified definition of "normal" capacity. In many jurisdictions, magazine capacity of certain firearms is legally restricted, such as it was under the United States' Federal Assault Weapons Ban, which defined a magazine capable of holding more than ten rounds of ammunition as a high capacity ammunition feeding device. This law expired in 2004 and there have since been multiple attempts to renew it[29] with no bill reaching the House floor for a vote. An attempt to only renew the limitations on large capacity magazines also failed.[30] Currently, in the United States, six states limit magazine capacities. The limits range from 5 rounds to 30 rounds.[31]
Magazine capacity is often limited by the design of the firearm in such cases as internal, tubular, or rotary magazines. In cases such as a detachable box magazine, capacity is limited only by its design. Some pistol and rifle magazines classified by gun control laws as "high capacity" are the factory standard magazines originally designed for use with their respective firearms. Reduced capacity magazines were created in response to enactment of the bans.[32]
At least six states (but not Connecticut) outlaw the sale of large-capacity magazines. Although the statutory definitions differ, typically these are magazines that can hold 10 or more rounds of ammunition (see Attachment II). -->>
http://www.cga.ct.gov/2007/rpt/2007-R-0217.htmAttachment II: States Prohibiting Large-Capacity Magazines
California* No more than 10 Cal. Penal Code § 12020(a)(2),(b)(c)25
Hawaii (applies to handguns only) No more than 10 Hawaii Rev. Stat. § 134-8(c)
Maryland* No more than 20 Md. Code Ann. Crim. Law § 4-305
Massachusetts* No more than 10 Mass. Gen. Laws ch. 140 §§ 121, 131M
New Jersey* No more than 15 N.J. Stat. Ann. §§ 2C: 39-9(h), 2C: 39-1(y), 2C: 39-3(j)
New York* No more than 10 N.Y. Penal Law §§ 265.00 (23), 265.02(8)