Please call the ATF and US Customs at your local field office or port of call to verify this information and get the appropriate forms.

(always get thier name and a method of contacting them directly)

Bureau of Alcohol, Tobacco & Firearms (ATF) 

ATF Field Division Offices

U.S. Customs and Border Protection

US Customs Service - Call the port of entry  and ask for a Customs Inspector

Moving to the U.S. - Personal firearms imported and shipped with household effects