; and (2) in paragraph (3)(E), by inserting 922(cc), after 922(w), . 523. Penalties Section 924(a)(1)(B) of title 18, United States Code, as amended by section 513 of this Act, is amended by striking or (w) and inserting (w), or (cc) . 524. Effective date The amendments made by this subtitle shall take effect on the date that is 90 days after the date of enactment of this Act. VI Firearm trafficking 601. Prohibition against multiple firearm sales or purchases (a) Prohibition Section 922 of title 18, United States Code, as amended by this Act, is amended by adding at the end the following: (dd) Prohibition against multiple firearm sales or purchases (1) Sale It shall be unlawful to sell, transfer, or otherwise dispose of a firearm, in of affecting interstate or foreign commerce, to any person who is not licensed under section 923 knowing or having reasonable cause to believe that such person purchased a firearm during the 30-day period ending on the date of such sale or disposition. (2) Purchase It shall be unlawful for any person who is not licensed under section 923 to purchase more than 1 firearm that has been shipped or transported in interstate or foreign commerce during any 30-day period. (3) Exceptions Paragraphs (1) and (2) shall not apply to— (A) a lawful exchange of 1 firearm for 1 firearm; (B) the transfer to or purchase by the United States, a department or agency of the United States, a State, or a department, agency, or political subdivision of a State, of a firearm; (C) the transfer to or purchase by a law enforcement officer employed by an entity referred to in subparagraph (B) of a firearm for law enforcement purposes (whether on or off duty); (D) the transfer to or purchase by a rail police officer employed by a rail carrier and certified or commissioned as a police officer under the laws of a State of a firearm for law enforcement purposes (whether on or off duty)