Many firearm parts — particularly frames, receivers, and barrels — are regulated as firearms themselves under the Gun Control Act and require ATF Form 6 import permits. Other components such as stocks, grips, and springs may not require a permit but are still subject to CBP scrutiny. Importers should confirm the regulatory status of each specific part with ATF before shipment.

Classification follows the heading of the weapon the part is principally designed or adapted for. If a component is designed specifically for a military weapon covered by heading 9301, it goes under 930591; if it is designed for a sporting rifle under heading 9303, it goes under 930520. A part that is genuinely interchangeable between both may require a principal-use analysis or a CBP binding ruling.