A licensee must record the type of firearm as a “frame” or “receiver” (as applicable) in the acquisition and disposition (A&D) record and on the ATF Form 4473. The licensee must also include in any record the make, model, and serial number of the frame or receiver.
As a frame or receiver is neither a shotgun nor a rifle, a licensee is prohibited from selling or delivering a frame or receiver to any individual the licensee knows or has reasonable cause to believe is less than 21 years of age.
[18 U.S.C. 922(b)(5), 27 CFR 478.11]