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
The clear and obvious takeaway:
The 2nd does not cover all 'arms" - just those that have a reasonable relationship to the preservation of the well-regulated militia.
I'm sorry -- I wasn't clear:
In 1939, what weapons do you suppose this included?
In 2022, what weapons do you suppose this includes?