TITLE 26 - US CODE - PART II - TAX ON TRANSFERRING FIREARMS

26 USC 5811 - Transfer tax

(a) Rate 
There shall be levied, collected, and paid on firearms transferred a tax at the rate of $200 for each firearm transferred, except, the transfer tax on any firearm classified as any other weapon under section 5845 (e) shall be at the rate of $5 for each such firearm transferred.
(b) By whom paid 
The tax imposed by subsection (a) of this section shall be paid by the transferor.
(c) Payment 
The tax imposed by subsection (a) of this section shall be payable by the appropriate stamps prescribed for payment by the Secretary.

26 USC 5812 - Transfers

(a) Application 
A firearm shall not be transferred unless
(1)  the transferor of the firearm has filed with the Secretary a written application, in duplicate, for the transfer and registration of the firearm to the transferee on the application form prescribed by the Secretary;
(2)  any tax payable on the transfer is paid as evidenced by the proper stamp affixed to the original application form;
(3)  the transferee is identified in the application form in such manner as the Secretary may by regulations prescribe, except that, if such person is an individual, the identification must include his fingerprints and his photograph;
(4)  the transferor of the firearm is identified in the application form in such manner as the Secretary may by regulations prescribe;
(5)  the firearm is identified in the application form in such manner as the Secretary may by regulations prescribe; and
(6)  the application form shows that the Secretary has approved the transfer and the registration of the firearm to the transferee. Applications shall be denied if the transfer, receipt, or possession of the firearm would place the transferee in violation of law.
(b) Transfer of possession 
The transferee of a firearm shall not take possession of the firearm unless the Secretary has approved the transfer and registration of the firearm to the transferee as required by subsection (a) of this section.