; and (2) in section 924(a)(2), by striking , or (o) and inserting (o), or (dd) . B Firearm silencers and mufflers ban 521. Definition Section 921(a)(3) of title 18, United States Code, is amended by striking (C) any firearm muffler or firearm silencer; or (D) and inserting or (C) . 522. Restrictions on firearm silencers and firearm mufflers (a) In general Section 922 of title 18, United States Code, as amended by section 517 of this Act, is amended by adding at the end the following: (ee) (1) Except as provided in paragraph (2), it shall be unlawful for a person to import, sell, manufacture, transfer, or possess, in or affecting interstate or foreign commerce, a firearm silencer or firearm muffler. (2) Paragraph (1) shall not apply to— (A) the importation for, manufacture for, sale to, transfer to, or possession by the United States or a department or agency of the United States or a State or a department, agency, or political subdivision of a State, or a sale or transfer to or possession by a qualified law enforcement officer employed by the United States or a department or agency of the United States or a State or a department, agency, or political subdivision of a State for purposes of law enforcement (whether on or off duty), or a sale or transfer to or possession by a campus law enforcement officer for purposes of law enforcement (whether on or off duty); (B) the importation for, or sale or transfer to a licensee under title I of the Atomic Energy Act of 1954 ( 42 U.S.C. 2011 et seq. ) for purposes of establishing and maintaining an on-site physical protection system and security organization required by Federal law, or possession by an employee or contractor of such licensee on site for such purposes or off site for purposes of licensee-authorized training or transportation of nuclear materials