Yes, the barrel length and overall length of a firearm are required pieces of information on an import permit application. Gun Control Act (GCA) regulations in 27 CFR 478.112(b) and Arms Export Control Act regulations in 27 CFR 447.42(a)(1) make this information a mandatory part of completing the permit application. Effective immediately, applications which lack this information, provide only a range (e.g., 18-24 inches), or which are non-specific (e.g., 18+ inches) with respect to barrel length and overall length will be returned without action by ATF for more information from the applicant.
Barrel length and overall length are important factors in helping ATF determine whether a firearm is importable, helping U.S. Customs and Border Protection reconcile a permit to the actual shipment during the release process at a port of entry, and may be useful in assuring that the correct duty is paid. In addition, the barrel length and overall length of a firearm are determining factors in whether a firearm is subject to the additional controls of the National Firearms Act (NFA). A shotgun having a barrel of less than 18 inches and an overall length of less than 26 inches and a rifle having a barrel of less than 16 inches and an overall length of less than 26 inches are classified as NFA weapons.