As nightfall does not come all at once, neither does oppression. In both instances, there is a twilight. And it is in such twilight that we all must be aware of change in the air, however slight, lest we become unwitting victims of the darkness. — Justice William O. Douglas, US Supreme Court (1939-75)
An interesting bit of history about Justice Douglas: He was not appointed to the Supreme Court until early April of 1939 & had missed the oral arguments in the U.S. vs. Miller appeal which occurred on March 15th, 1939. So he recused himself from offering any opinion in regards to that case. It would have been interesting to see what his take on the matter was, especially considering he served in WW1 where, like all wars, short barreled shotguns were used in a military capacity.
The JPFO has a decent summary of the circumstances surrounding U.S. vs. Miller written by Richard Stevens & Aaron Zelman.