It's actaully worse than you think because in addition to Federal law, each and every state has its own rules.

Like California and Massachusetts have some of the strictest gun laws in the nation. New Hampshire - where I live - is open carry. So long as you're not concealing it you don't need a license to own or carry in public so long as it's not in a threatening manner. You pull that stunt in Massachusetts and you go to jail as you must be licensed.

California has strict laws about magazine capacity that don't exist anywhere else in the US.

It's possible to travel 60 miles, and go through four different regions of different gun control laws. In the same flipping nation! I live a half hour from one of the most obsessively controlling states in the nation, and an equal distance from one of the most liberal! If I wanted to take a weapon with me on a normal "day trip" I can cross three different legal zones in under an hour! And let me just say that again, in the same country!

We have this pesky thing called the 10th amendment... and it causes a lot of confusion in regards to the 2nd.

"The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people."

You want to know how crazy US gun laws are? The only part of a firearm that's considered 'the gun" is the reciever. Everything else is just "parts" you can buy and sell unrestricted,. Including barrels. Which is why 3d printing or milling aluminum recievers is the new go-to for unregistered firearms. All you need is that one part, and the rest is free, clear, and largely unregulated.