That right is neither absolute nor unlimited doesn't mean that there aren't clear lines that the government isn't allowed to overstep. The First Amendment is neither absolute nor unlimited, as well, but the bar is extremely high in practice.
As far as ownership of military grade arms - that stems directly from the wording of the Second, and is given some validation by the judicial commentary in the Miller decision (that's the one where the court ruled that the defendant did not have a constitutional right to possess a sawed-off shotgun, on the basis that it is not a common military weapon). The exact boundaries of 2A are yet to be determined, but the wording of Heller strongly imply that "assault weapons" are protected - it specifically cites "... in common use at the time" as one of the criteria for protection, and it would be very hard to argue that a firearm of which 9 million were made (and sold) in 8 past years alone is not "in common use".
It would be the ultimate irony if this argument that it's all about the militia wins the day, but combined with individual interpretation of the right - which would imply that every citizen has the right to own military grade weapons (even fully automatic, since that's what militaries use, after all) - and only them; not hunting rifles etc.