I think you did a great job explaining. From those levels of scrutiny, it seems that the only type that has been used by the judiciary for 2A cases has been Rational basis.
Not true. The examples I gave were intentional.
The basic right to own a gun can be subject to strict scrutiny. This was the point of
Heller. States/DC/Territories cannot outright prohibit gun ownership, like DC did with handgun ownership up until
Heller. Note that while
Heller did not come right out and say "RKBA cases should be held to strict scrutiny",
Heller ruled the RKBA as fundamental. More on "fundamental" rights below. The trouble we've been having is expanding
Heller's protection to other kinds of guns, like MSRs. Also note that some states, such as Louisiana, automatically require strict scrutiny to be applied in RKBA cases:
The Louisiana Supreme Court on Tuesday upheld a state law that forbids felons from possessing firearms, ruling that lawmakers did not intend to invalidate the state’s weapons laws when they proposed a constitutional amendment declaring gun ownership a fundamental right.
Justice Jeff Hughes wrote in a unanimous opinion that the state’s ban on the possession of firearms by convicted felons “is not affected” by the constitutional language approved by voters in 2012.
The justices also found that the law, R.S. 14:95.1, withstood a legal test known as “strict scrutiny,” the highest level of judicial review, which became necessary after voters in 2012 overwhelmingly approved constitutional language that gave Louisiana the strongest gun-rights laws in the nation.
La. Supreme Court upholds gun restrictions
I gave the example of concealed carry laws with intermediate scrutiny because self-defense has a natural law basis. The concept of self-defense dates back to time immemorial and is part of our Anglo-American common law tradition. However, the right to concealed carry is for the most part a modern one (most states enacted concealed carry laws between 1900-1990, with a big chunk towards the 70s-90s). Courts typically will do some form of historical analysis. You can see this in
Heller when Scalia pulls out Dr. Johnson's Dictionary for definitions of terms like "bear" and "arms", but the (liberal) dissent instead used the modern Oxford dictionary. What Scalia was trying to do was to view the Second Amendment in the same mindset as the Founders to derive their intent.
This also brings up another extremely important part of constitutional analysis: how broadly the right is defined. Let's use the Maura Healey unlawful ban of MSRs as an example. A plaintiff against Maura would want to define the right at stake as broadly as possible, such as "the right to keep and bear arms." This would give the plaintiff more ammunition, better history and case law on their side, and encourages the court to be more cynical about the regulation, like how Justice Kennedy in
Obergefell typified the right to same sex marriage as more akin to the right to live with dignity, rather than the right of two same sex individuals to receive preferential tax status. On the flip side, the government wants to define the right as narrowly as possible. Sticking with the Maura example, Mass would argue that the right at stake is the ability to own an already heavily-regulated and dangerous weapon of war, similar to a machine gun and
US v. Miller, which upheld the NFA 34.
United States v. Miller - Wikipedia
But yes, rational basis gets used a lot in 2A cases. Again though, it depends on the facts of the case and how broad the right is. Which finally brings up one more part of the analysis: whether or not the right is fundamental. If a right is fundamental, like say the right to bodily integrity against impermissible government searches and seizures, the right of minorities to participate in the governmental process, and the right to basic gun ownership, then the court applies strict scrutiny. A fundamental right is typically something that's immutable, or put another way, something the plaintiff cannot control. The plaintiff cannot chose to be an African American in 1960s Mississippi who gets a felony conviction for looking at a white woman - he's born as a black person, his skin color doesn't change. Which is why a lot of RKBA cases get rational basis: there is no fundamental right to machine gun ownership, per
Miller.
So to back up and clarify:
If a right is fundamental and the plaintiff has an immutable trait, strict scrutiny usually applies. States can enact constitutional amendments requiring courts to apply strict scrutiny in RKBA cases. If the right is not fundamental, then the court will apply a lesser standard, such as intermediate scrutiny or rational basis. To determine if the right is fundamental, courts conduct a historical analysis and look at the facts to strike a balance between the broad wording of the plaintiff and the narrow wording of the government.
I am not a lawyer, this does not constitute legal advice, and I strongly encourage everyone to read some constitutional law cases online. Most state supreme courts and SCOTUS post newly decided cases online, free for all to view. Cornell law school also does a good job posting important cases. Oyez gives the quick and dirty summary. When people post that the common law is dead, they're posting out of ignorance. There's a whole different issue of how much judicial activism a court should use to strike down laws that restrict rights. Unfortunately for conservatives/libertarians, similarly-minded judges are often in favor of judicial restraint.