No, except that frames or receivers of firearms are "firearms" as defined in the law and are subject to the same controls as complete firearms. Certain parts of silencers and machineguns are also regulated as firearms under the GCA, as well as under the National Firearms Act (NFA).
[18 U.S.C. 921(a)(3), (23) and (24); 26 U.S.C. 5845; 27 CFR 478.11 and 479.11]