The National Firearms Act — as applied to transporting in interstate commerce a 12-gauge shotgun with a barrel less than 18 inches long, without having registered it and without having in his possession a stamp-affixed written order for it — was not unconstitutional as an invasion of the reserved powers of the States and did not violate the Second Amendment of the United States Constitution.
My understanding is that the lower court had declared that short barreled shotguns had a military use and therefore could not be taxed (restricted) under the NFA. The US Supreme Court remanded that District Court decision which had supported the legality of short barreled shotguns. The USSC upheld the NFA.
The notion that such shotguns had no military use was a central (and erroneous) determinant.
In the absence of any evidence tending to show that possession or use of a 'shotgun having a barrel of less than eighteen inches in length' at this time has some reasonable relationship to the preservation or efficiency of a well regulated militia, we cannot say that the Second Amendment guarantees the right to keep and bear such an instrument. Certainly it is not within judicial notice that this weapon is any part of the ordinary military equipment or that its use could contribute to the common defense.
US v Miller, 307 U.S. 174 (1939)
So, "[absent] any evidence," the Supreme Court "cannot say" that a short barrel shotgun " has some reasonable relationship to the preservation or efficiency of a well regulated militia," or "is any part of the ordinary military equipment or that its use could contribute to the common defense."
The Supreme Court reversed the judgment below. It had to in order to provide a venue for further judicial findings. If the judgment had stood, there would be no indictment, and no basis for the court below to hear any argument or obtain any further evidence.
The "absent any evidence" part is important, because it is the reason why the Supreme Court could not say. Court now cherry pick that part out, and roughly assert that SCOTUS had evidence and said that a short barrel shotgun has no relationship to the preservation or efficiency of a well regulated militia, is no part of military equipment, and use of a SBS cannot contribute to the common defense. That is an incorrect read.