"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."
Guns. Lots of guns.
There is no specification of the Arms protected by the Second Amendment, and the fact that nobody seriously proposes either that the Amendment is restricted to the possession of muskets actually available at the time of the writing or expands to protect private ownership of nuclear or biogenic weapons indicates that everybody already accepts the premise that Arms are a selective category, and even that considerations of safety can determine weather particular weapons can be banned or not.
Given the speed with which gun advocates inevitably point to the fact that the banning of guns will not eliminate murder since many artifacts can be used as lethal weapons -- table knives, golf clubs, fuel-fat jets -- it should be noted that, perhaps contrary to purpose, gun advocates are demonstrating through such arguments that even the banning of all guns altogether (which is a position few to none advocate at all) would leave citizens quite free to keep and bear any number of forms of Arms.
Neither is it true nor Constitutionally indicated that unrestricted access or private ownership are the only conditions satisfying the state of "keep[ing] and bear[ing]" of Arms that is Constitutionally protected. That access to guns be circumscribed by mandated security standards, locking mechanisms, restricted locations, or even contracted out to public officials working in the public interest need not necessarily be regarded as violations of "keep[ing] and bear[ing] Arms" under certain possible interpretations of the Constitution (not all of which I personally regard as plausible, nor would necessarily endorse myself, I'm just pointing out that the phrase is not one with a singular easily legible interpretation).
I personally think that the initial framing of the Constitutional provision by considerations of "a well regulated Militia" (you will notice that the word "regulation" appears right there in the very Amendment itself, and is clearly not thought inherently to infringe the right of the people to keep and bear Arms that follows it) in an era of precarious national security without reliable standing armies is enormously significant to a proper understanding of the Second Amendment, and one that is quite catastrophic to the arguments of so-called gun advocacy politics. But I also think there is little rhetorical force in any of that, true though it may be, because I don't think Americans generally have much awareness of the concrete historical context the phrase references nor do they much care for arguments that take such contextual and intentional considerations into account in the first place. I think Americans are more interested in the plausible applicability of Constitutional principles and phrases to contemporary problems and conditions than their initial ones, frankly. As someone who regards the Constitution as a living document I don't even think that is a particularly bad thing all told.
I will say, however, that I believe there is a profound and paranoid anti-governmental mentality at the heart of the most aggressive gun advocacy, while the Amendment deployed in the service of this anti-governmentality actually originally expressed a profoundly patriotic support of the need to defend the government from enemies. The commandeering of the Second Amendment in the service of a white-racist patriarchal anti-governmental anti-civilizational mindset declaring government of by and for the people itself to represent an antithetical occupational force represents a profound perversion of the spirit of the Amendment, and of the Document of which it is a part at the deepest imaginable level.