26 USC § 4181
Imposition of tax
through Public Law 119-27, except Public Law 119-21
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.