The Supreme Court of the United States ruled that the NFA was constitutional in the 1939 case U.S. v. Miller

Yes, but:

https://en.wikipedia.org/wiki/United_States_v._Miller

The defendants Jack Miller and Frank Layton were indicted on charges of unlawfully and feloniously transporting in interstate commerce from Oklahoma to Arkansas an unregistered double-barrel 12-gauge shotgun having a barrel less than 18 inches in length, in violation of the National Firearms Act, 26 U.S.C.S. § 1132c et seq. ("Act"). At trial in federal district court, the defendants filed a demurrer to the indictment alleging that the Act was not a revenue measure but an attempt to usurp police power reserved to the states and so was unconstitutional. Defendants further argued that the Act violated the Second Amendment to the United States Constitution. The district court held that the section of the Act that made it unlawful to transport an unregistered firearm in interstate commerce was unconstitutional as violative of the Second Amendment. It accordingly sustained the demurrer and quashed the indictment. The government took a direct appeal to the Supreme Court.

In reality, the district court judge, Heartsill Ragon, was in favor of the gun control law and ruled the law unconstitutional because he knew that Miller, who was a known bank robber and had just testified against the rest of his gang in court, would have to go into hiding as soon as he was released. He knew that Miller would not pay a lawyer to argue the case at the Supreme Court and would simply disappear. Therefore, the government's appeal to the Supreme Court would surely be a victory because Miller and his attorney would not even be present at the argument.[2][3]

Miller didn't even show up, defense council didn't show up, it was a case that effectively wasn't even argued.