I'm not a constitutional expert. I've read the document and the "Federalist Papers" as written by our founding fathers in support of the Constitution. From what I glean, debate over a federal army was hot and states' rights were paramount.
The newly formed nation did not want to risk a standing federal army which could overthrow the still-forming government. The Continental Army was mostly disbanded in 1783 after the revolution ended. The states maintained their own militia for their defense.
"A well-regulated militia, composed of the body of the people, trained to arms, is the proper, natural, and safe defense of a free state; that standing armies, in time of peace, should be avoided as dangerous to liberty; and that in all cases the military should be under strict subordination to, and governed by, the civil power." This was a popular opinion of the framers of the Constitution.
The Second Amendment reads, "A well regulated militia, being necessary to the security of a free State, the right of the People to keep and bear arms shall not be infringed."
If we objectively read the arguments over the amendment prior to its ratification, I believe it is allowing the states to maintain their militia. These militia have morphed into the National Guard. Logically therefore, the Second Amendment affords the "right to bear arms" to the guards and Army Reserves.
I know that most gun owners are responsible citizens, but does the average citizen out there really need assault weapons? NO! ENOUGH!