You see, despite the fact that firearms are the most effective, efficient, practical means with which to keep and bear arms, they are, as that simple fact implies, not the actual point of the 2nd Amendment, but only one means of our carrying out what is protected by that amendment. Despite what often seems to be the best efforts of those on all sides, the 2nd Amendment is not primarily about gun rights - in fact there is no such thing as 'gun rights'. Nope. Not. Things, of course, do not have rights, but by claiming a right to things, it eventually eliminates all rights, because it means that someone, somewhere, is obligated to supply what others have claimed a right to, whether they want to, or not - that's not how rights work! BTW, that's the same strategy behind demands that 'Healthcare' be treated as a 'Right'.
What the 2nd Amendment is all about, is securing the right of each individual to be able to act in the defense of their community, persons, property and interests, by freely choosing the personal arms which in their judgment is best suited to that task. That's possible, because the 2nd Amendment assures We The People, that the government will neither infringe upon those actions we deem necessary to take, nor will it make any law that would come between ourselves and those arms we may choose from in order to act.
With that in mind, take note of the word 'Arms' in the language of the 2nd Amendment :
'...the right of the people to keep and bear Arms, shall not be infringed.'
And no, the 2nd Amdt is not about 'bearing arms against foreign militias'