27 CFR § 447.45 - Importation.
(a) Articles subject to the import permit procedures of this subpart imported into the United States may be released from Customs custody to the person authorized to import same upon his showing that he has a permit for the importation of the article or articles to be released. For articles in Categories I and III imported by a registered importer, the importer will also submit to Customs a copy of the export license authorizing the export of the article or articles from the exporting country. If the exporting country does not require issuance of an export license, the importer must submit a certification, under penalty of perjury, to that effect.
(2) The ATF Form 6A must contain the information requested on the form, including:
(i) The name, address, and license number (if any) of the importer;
(ii) The name of the manufacturer of the defense article, or “privately made firearm” (if a firearm privately made in the United States);
(iii) The country of manufacture;
(iv) The type;
(v) The model;
(vi) The caliber, gauge, or size;
(vii) The serial number in the case of firearms, if known; and
(viii) The number of defense articles released.
(b) Within 15 days of the date of their release from Customs custody, the importer of the articles released will forward to the address specified on the form a copy of Form 6A on which will be reported any error or discrepancy appearing on the Form 6A certified by Customs and serial numbers if not previously provided on ATF Form 6A.