As Answered on Quora

The classical liberal theory of the state expects citizens to defend themselves while ceding to the state the right to retaliate after the fact of any conflict, or to seek recompense for any rights violently and criminally violated. The point of police and courts is not to protect you, but to protect everyone from those seeking vigilante justice after instances of perceived harms.

So classical liberals will, by their very nature, support an armed citizenry. Anyone who wishes to disarm citizens is not a classical liberal. I would argue, further, that the anti-armament advocate is not any kind of liberal. This and the rights of free speech, conscience, press, and assembly, constitute the demarcation between liberals and non-liberals.

A person who may not arm and defend him- or herself is not free. A state that fears its armed populace is not a republic.

Contrariwise, a people that routinely extracts private justice in secret is not free, either. It is, instead, well on its way to tyranny or chaos. A state that exacts retribution or redress in secret is also tyrannical, just as is a state that prevents its people from self-defense.

Now, this does not mean that a free society cannot support private law justice. We still have elements of that now, especially in civil law. But secretive, hidden retaliation leads to vendetta and civil warfare, a sort of Hobbesian war of all against all. The key to justice, in republican theory, depends upon the public, open adjudication of potentially violent disputes. And that is the basic idea of a republic, according to classical liberal theory. You can find this theory in the writings of John Locke, early theorists of the American Constitution like John Taylor of Caroline, and in the work of J. S. Mill and Herbert Spencer.

So, some form of armament must be ready in the hands of the citizenry of a republic. Some kinds of armaments might be disallowed (no nuclear warheads in basements!) but I think the basic rule should be — and would be among all informed, honest liberals — that the citizenry must not be prohibited from owning and carrying any weapons that the state, in its policing, owns and carries.

Yes, classical liberals would be, almost certainly and by definition, “pro-gun.”