26 U.S.C. § 4181: Imposition of tax

There is hereby imposed upon the sale by the manufacturer, producer, or importer of the following articles a tax equivalent to the specified percent of the price for which so sold: Articles taxable at 10 percent— Pistols. Revolvers. Articles taxable at 11 percent— Firearms (other than pistols and revolvers). Shells, and cartridges.