; and (2) in subsection (d)(1), by striking or (k) and inserting (k), (aa), (bb), (cc), (dd), or (ee) . 4. Modernization of the prohibition on un­de­tect­able firearms Section 922(p) of title 18, United States Code, is amended— (1) in paragraph (1)— (A) in the matter preceding subparagraph (A), by striking any firearm ; (B) by amending subparagraph (A) to read as follows: (A) an undetectable firearm; or ; and (C) in subparagraph (B), by striking any major component of which, when subjected to inspection by the types of x-ray machines commonly used at airports, does not generate and inserting the following: a major component of a firearm which, if subjected to inspection by the types of detection devices commonly used at airports for security screening, would not generate ; (2) in paragraph (2)— (A) by amending subparagraph (A) to read as follows: (A) the term undetectable firearm means a firearm, as defined in section 921(a)(3)(A), of which no major component is wholly made of detectable material; ; (B) by striking subparagraph (B) and inserting the following: (B) the term major component , with respect to a firearm— (i) means the slide or cylinder or the frame or receiver of the firearm; and (ii) in the case of a rifle or shotgun, includes the barrel of the firearm; and ; and (C) by striking subparagraph (C) and all that follows through the end of the undesignated matter following subparagraph (C) and inserting the following: (C) the term detectable material means any material that creates a magnetic field equivalent to or more than 3.7 ounces of 17–4 pH stainless steel. ; (3) in paragraph (3)— (A) in the first sentence, by inserting , including a prototype, after of a firearm ; and (B) by striking the second sentence; and (4) in paragraph (5), by striking shall not apply to any firearm which and all that follows and inserting the following: “shall not apply to— (A) any firearm received by, in the possession of, or under the control of the United States