; (2) in section 922(b)— (A) in paragraph (1), by striking shotgun or rifle the first place it appears and inserting shotgun, rifle, firearm silencer or firearm muffler, ; and (B) in paragraph (3), by striking rifle or shotgun and inserting shotgun, rifle, firearm silencer or firearm muffler ; and (3) in section 923(i)— (A) by striking Licensed and inserting the following: (1) In the case of a firearm other than a firearm silencer or firearm muffler, licensed ; and (B) by adding at the end the following: (2) In the case of a firearm silencer or firearm muffler, licensed importers and licensed manufacturers shall identify by means of a serial number engraved or cast on the keystone part of the firearm silencer or firearm muffler, in such manner as the Attorney General shall by regulations prescribe, each firearm silencer or firearm muffler imported or manufactured by such importer or manufacturer, except that, if a firearm silencer or firearm muffler does not have a clearly identifiable keystone part or has multiple keystone parts, licensed importers or licensed manufacturers shall submit a request for a marking variance to the Attorney General. The Attorney General shall grant such a request except on showing good cause that marking the firearm silencer or firearm muffler as requested would not further the purposes of this chapter. . 1507. Imposition of tax on firearm silencers or firearm mufflers (a) In general Section 4181 of the Internal Revenue Code of 1986 is amended by adding at the end of the list relating to Articles taxable at 10 percent the following: Firearm silencers or firearm mufflers. . (b) Firearm silencers