From Dalton:
Finally, the government argues that the Gun Control Act, of which section 922(o) is a part, should not be viewed as repealing the National Firearms Act, citing a provision of the Gun Control Act passed in 1968 to that effect. The court in Rock Island Armory rejected the same government argument, observing that "the 1968 Congress cannot bind the Congress of 1986, which decided to ban transfer and possession of machineguns. P.L. 99-308, 100 Stat. 453 (May 19, 1986). Further, a Congressional declaration in 1968 does not solve a constitutional problem which arose in 1986. The ban enacted in 1986 and the government's refusal to accept registrations and tax payments, simply left the registration requirements with no constitutional basis."
And US v. RIA:
The enactment of 18 U.S.C. sec. 922(o) in 1986 removed the constitutional legitimacy of registration as an aid to tax collection. This is because the government interprets and enforces sec. 922(o) to disallow registration, and refuses to collect the tax. Farmer v. Higgins, 907 F.2d 1041, 1042-44 (11th Cir.1990), cert. denied, - U.S. - , III S.Ct. 753, 112 L.Ed.2d 773 (1991). Thus, sec. 922(o) undercut the constitutional basis of registration which had been the rule since Sonzinsky.
Finally, the prosecution quotes an enactment passed in 1968 that the provisions of Title I of the Gun Control Act shall not modify or affect the National Firearms Act. (Footnote 15) However, the 1968 Congress cannot bind the Congress of 1986, which decided to ban transfer and possession of machineguns. P.L. 99-308, 100 Stat. 453 (May 19, 1986). (Footnote 16) Further, a Congressional declaration in 1968 does not solve a constitutional problem which arose in 1986. The ban enacted in 1986, and the government's refusal to accept registrations and tax payments, simply left the registration requirements with no constitutional basis. It is the duty of the judiciary to declare such laws unconstitutional. Marbury v. Madison, I Cranch. 137, 176-77, 2 L.Ed. 60 (1803).
In sum, since enactment of 18 U.S.C. sec. 922(o), the Secretary has refused to accept any tax payments to make or transfer a machinegun made after May 19, 1986, to approve any such making or transfer, or to register any such machinegun. As applied to machineguns made and possessed after May 19, 1986, the registration and other requirements of the National Firearms Act, Chapter 53 of the Internal Revenue Code, no longer serve any revenue purpose, and are impliedly repealed or are unconstitutional. Accordingly, Counts l(a) and (b), 2, and 3 of the superseding indictment are
DISMISSED.
Reads to me like the entirety of 922(o) was struck as it lost the tax nexus that made it constitutional.
The court failed to take that last step.
They found that 922(o) replaced the corresponding part of NFA. They did not go so far as to then find 922(o) unconstitutional per lack of nexus.
If a court DOES repeal 922(o) for any reason, the corresponding part of NFA is revived.