When folks ask for primary sources regarding the U.S. Constitution, I tend to turn to the excellent The Founders' Constitution by the University of Chicago Press, which provides primary source documents that contribute to any discussion on the merits (or demerits) of any Constitutional clause. It last came up in a discussion regarding America's lack of peerage about two months ago.

In any event, the Second Amendment's "defense against tyranny" argument is rooted in British common law, as it existed at the time of the American Revolution. As early as the 1328 Statute of Northampton, there were laws protecting the right to bear arms. These rights were initially installed as a means to a common defense ─ to protect one's hearth and kin would require weapons that could be mustered at a moment's notice.

The right to possess arms was gradually extended to encompass the notion of being able to carry those arms as well. In 1686, there was the case of Sir John Knight, who was acquitted of charges filed against him for carrying guns into St. Michael's church in Bristol.

One of the key documents we have into the minds of the Founders is William Blackstone's Commentaries on the Laws of England, published in first edition in 1765. This text was widely distributed and considered one of the top references at the time of the Revolution. Blackstone has this to say about the right to possess arms for defense:

"(it) is indeed a public allowance, under due restrictions, of the natural right of resistance and self-preservation, when the sanctions of society and laws are found insufficient to restrain the violence of oppression."

Emphasis mine in that quote.

This particular thought was one of the guiding principles behind the Declaration of Independence and the state constitutions drawn up as the American Revolution began: that armed resistance was a natural outgrowth necessary to "restrain ... oppression" brought about by the failure of the British government to redress American concerns.

In 1776, shortly after the Declaration was signed, the colony of Pennsylvania held a constitutional convention that produced a remarkable document by September. (That Benjamin Franklin was one of the key forces behind it should be no surprise.) Article XIII of this 1776 constitution's declaration of rights states:

"That the people have a right to bear arms for the defence of themselves and the state; and as standing armies in the time of peace are dangerous to liberty, they ought not to be kept up; And that the military should be kept under strict subordination to, and governed by, the civil power.

This remarkable clause encapsulates a lot of the beliefs present at the time: That standing armies were forces of reaction and thus dangerous to personal liberty, that mobilized militias should be held accountable to civilian authority, and that personal possession of weapons should be guaranteed as a backstop against tyranny. While the U.S. Constitution ultimately decided against a proscription against a standing military, antimilitarist sentiment was a driving force in the United States as late as 1941.

You can see this sentiment in debates over the founding (and funding) of West Point and the establishment of the U.S. Navy. The cost of a military and its ability to spawn conservative, reactionary power, was seen as a threat to representative democracy.

In 1803, after the founding of the United States, Blackstone reissued his commentaries "With Notes of Reference to the Constitution and Laws of the Federal Government of the United States and of the Commonwealth of Virginia." Here, the snake is eating its tail ─ an author who inspired portions of the U.S. Constitution was himself being inspired by that constitution. This is what the new version has to say about the right to bear arms:

"This may be considered as the true palladium of liberty. . . . The right of self defence is the first law of nature: in most governments it has been the study of rulers to confine this right within the narrowest limits possible. Wherever standing armies are kept up, and the right of the people to keep and bear arms is, under any colour or pretext whatsoever, prohibited, liberty, if not already annihilated, is on the brink of destruction."

Perhaps this is too simple an answer compared to the others, but I believe what you're specifically looking for is the context provided by the preamble to the Bill of Rights.

Rights were declaratory and restrictive clauses added to the Constitution "in order to prevent misconstruction or abuse of its powers."

The 2nd amendment being one of those rights with its own declaratory and restrictive clause.

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Text from Preamble:

THE Conventions of a number of the States, having at the time of their adopting the Constitution, expressed a desire, in order to prevent misconstruction or abuse of its powers, that further declaratory and restrictive clauses should be added: And as extending the ground of public confidence in the Government, will best ensure the beneficent ends of its institution.

Text from 2nd Amendment:

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.