Mikeb302000 has a post up about U.S. v. Miller. Comments are moderated so I’m putting my comment (with a couple minor grammar edits) here for safe keeping and better visibility:
Shotguns having a barrel of less than eighteen inches in length were not well known as being used by the militia and military. Hence because Miller lawyer was not there to present such evidence he lost.
If Miller had been charged with not registering and paying a tax on a machine gun then he probably would have won. This is because it is well known that “possession or use” of machine guns have a “reasonable relationship to the preservation or efficiency of a well regulated militia”.