The US Constitution does not say that there can be no laws about guns, but it does say that Americans have the right to bear arms because a militia is a necessary part of national defense (which is to say, if America were to be invaded, the invaders would have to face not just the US armed forces, but an armed citizenry as well). In the end, it is the Supreme Court which will rule on what is or is not constitutional.
If this law violates the right to bear arms given in the 2nd Amendment, the law is unconstitutional.
Who can declare laws unconstitutional
They are called "unconstitutional laws".
The Legislative Branch sometimes passes unconstitutional laws, but they're not supposed to. None of the branches is authorized to create unconstitutional laws.
by allowing unconstitutional laws to be challenged and overturned
They are called "unconstitutional laws".
They are called "unconstitutional laws".
no
A law which conflicts with a constitution is said to be unconstitutional.
unconstitutional
Laws
Breaking the highest laws of America
Ex post facto laws are unconstitutional. Those are laws that proscribe a behavior or act after it has been commenced or occurred.