; (4) a second hand grip; (5) a manufactured weight of 50 ounces or more when the pistol is unloaded; and (6) a semiautomatic version of an automatic firearm. 6. Construction Nothing in this Act shall be construed as limiting the ability of a State to enact more restrictive gun-related laws, or bans on firearm receiver castings, firearm receiver blanks, assault weapon parts kits, or machinegun parts kits. 7. Effective date (a) In general Except as provided in subsection (b), this Act and the amendments made by this Act, shall take effect 180 days after the date of the enactment of this Act. (b) Exceptions Subsections (a), (b), and (d), and the second sentence of subsection (c)(2), of section 923A of title 18, United States Code, as added by the amendment made by section 4(a) of this Act, shall take effect on the date of the enactment of this Act.