I know, but the Supreme Court opinion indicated that they implicitly did, when their opinion stated:
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.
...
We are unable to accept the conclusion of the court below and the challenged judgment must be reversed. The cause will be remanded for further proceedings.
Since there were no "further proceedings" we can never know what might have occurred at them. But surely Miller's lawyer, had Miller still been among the living, would have brought in evidence that short barreled shotguns, even if not the exact type used by Miller, had indeed been at one time "part of the ordinary military", and not so long before then either.
In the civil war, and Indian wars after and before, the shotgun, usually a double barrel, was a common weapon of calvary troops.
BTW, the Winchester model 97 had an 18" barrel not a 20". (see also this article from Global Security But the reason it was that long was to give it a respectable magazine capacity, since their would be no point the barrel being shorter than the magazine tube. (Some barrel length went to the bayonet attachment as well, since the base of the bayonet fits up against the end of the magazine.
