This work slightly modified was originally published by me on Quora.
No it is unconstitutional.
It violates the US Constitution in several specific, separate and distinct manners.
Violation of the no ex post facto clause in Article I section 9 paragraph 3 -
No Bill of Attainder or ex post facto Law shall be passed.
An ex post facto law is a law criminalizing something you did in the past that was not criminal at the time, thus buying a high capasity magazine 20 years ago was not a crime then, so you cannot punish owning it now, that would include seizing the property which is punishment and seperatly a violation of the 5th Amendment see below.
Violation of the 2nd Amendment
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.
To all the typical comments, it is explicitly stated as a right of the people, not right of the militia or state. Further “well regulated” meant nothing like government regulation, it meant functioning properly, or as expected, a clock was “well regulated” if it kept good time.
Violation of the 5th Amendment.
No person shall be held to answer for a capital, or otherwise infamous crime, unless on a presentment or indictment of a Grand Jury, except in cases arising in the land or naval forces, or in the Militia, when in actual service in time of War or public danger; nor shall any person be subject for the same offence to be twice put in jeopardy of life or limb; nor shall be compelled in any criminal case to be a witness against himself, nor be deprived of life, liberty, or property, without due process of law; nor shall private property be taken for public use, without just compensation.
No just, reasonable or fair compensation was offered, nor is the private property taken for public use. Denial of the right to own such property is not within the scope of authority of the government to take private property for public use.
Taking the magazine in a real military or police emergency for military or police urgent use, and giving it back at the end of the emergency would be constitutional. The state has no authority to disarm the people in general, such acts are not legitimately within the state government scope of authority.
Violation of Amendment XIV section 1
All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the State wherein they reside. No State shall make or enforce any law which shall abridge the privileges or immunities of citizens of the United States; nor shall any State deprive any person of life, liberty, or property, without due process of law; nor deny to any person within its jurisdiction the equal protection of the laws.
The 2nd Amendment right to bear arms is a privilege/immunity of all American citizens. Taking someone’s property without due process is unconstitutional.
Due process involves a court case in which the accused must be found guilty or at least liable as regards a proper and constitutional law. Due process is NOT a state legislature declaring that a property a person has owned for many years is illegal and must now be surrendered without compensation.
This behavior by the California legislature is arguably illegal by federal law.
https://www.law.cornell.edu/uscode/text/18/241
If two or more persons conspire to injure, oppress, threaten, or intimidate any person in any State, Territory, Commonwealth, Possession, or District in the free exercise or enjoyment of any right or privilege secured to him by the Constitution or laws of the United States, or because of his having so exercised the same; or
If two or more persons go in disguise on the highway, or on the premises of another, with intent to prevent or hinder his free exercise or enjoyment of any right or privilege so secured—
They shall be fined under this title or imprisoned not more than ten years, or both; and if death results from the acts committed in violation of this section or if such acts include kidnapping or an attempt to kidnap, aggravated sexual abuse or an attempt to commit aggravated sexual abuse, or an attempt to kill, they shall be fined under this title or imprisoned for any term of years or for life, or both, or may be sentenced to death.
FYI a federal judge issued a stay on the magazine confiscation last summer.
This is winding through the courts now.