Why thank you, Nico. I do own more than the average amount of firearms, and I shoot them all (well, I'm still looking for Brit .410 shotshells for an old Enfield).
I see no contradiction between liberalism and guns. In 1776 it was the liberals who wanted independence from British rule. The conservatives back then were the Tories who didn't want to change things, they were afraid of change.
Sorry, I'm off topic.
Back on topic; Addressing the O.P.'s question of how do states get to regulate areas covered in the federal Const. The Constitution's Bill of Rights, as originally drafted, did not limit the states, only the federal gov. In 1789, states could limit free speech by their citizens. States could quarter soldiers in private homes. The federal gov. could not do such, but states could.
When the Const. was written, people were fearful of a powerful federal gov., but they trusted their (respective) states to do the right thing. As such, the Const. did several things. First, it enumerated the rights which the states gave up to be in the union (had to have a republican form of government, submitted to taxation, gave up the right to enter into treaties with other nations, etc.,)
Secondly, the Const. limited the federal gov. to only those powers granted to it in the document (& amendments). Unless otherwise specified, each state had the power to tend to their own affairs, they were not limited by the federal Const., but rather their own (respective) constitutions. This was re-affirmed in the 10th Amendment.
Thirdly, the Const. protected individual rights which existed before the Const. was drafted. This was enshrined in the 9th Amen. Examples of these rights were such as the right to privacy (it was not mentioned in the Const. because it was implicitly understood to be a right held by all, so why mention what everyone already knew?), the right to seek legal redress in a court for civil harms (torts) caused by other individuals, the right marry, etc.
Now all this went out the window with the enactment of the 14A. A clause in that Amendment (No state shall...equal protection of the laws) allowed SCOTUS to "incorporate," one at a time, the amendments contained in the Bill of Rights. That means those rights now limit the states on what restrictions they can impose on their citizens. The most recent of which is the right to own a handgun, coming from the McDonald decision.
And then there is the matter of the Commerce Clause & SCOTUS perverting the original intent of the framers. Not to mention the SCOTUS & the Neccessay & Proper clause.
Sorry to waste space, but perhaps I didn't as there could be some here who are not familiar with our Constitution's history. Eeeh.