[JimDandy]

Originally Posted by SHR970

we would then be able to use it to attack and overturn a host of laws and / or force substantial modification.

I think that's skipping a step. First you have to get something so prohibited classified as an "arm" THEN you can use Peruta (in the 9th as it's currently ruled) to get or force some sort of method to carry it.

There are two "tests" that I know of. The older one from United States v. Miller 307 US 174 said:

Originally Posted by MR. JUSTICE McREYNOLDS

With obvious purpose to assure the continuation and render possible the effectiveness of such forces, the declaration and guarantee of the Second Amendment were made. It must be interpreted and applied with that end in view.

In the absence of any evidence tending to show that possession or use of a "shotgun having a barrel of less than eighteen inches in length" at this time has some reasonable relationship to the preservation or efficiency of a well regulated militia, we cannot say that the Second Amendment guarantees the right to keep and bear such an instrument. Certainly it is not within judicial notice that this weapon is any part of the ordinary military equipment, or that its use could contribute to the common defense. Aymette v. State, 2 Humphreys (Tenn.) 154, 158.

Then in Heller the Supreme Court, without actually repudiating Miller (as far as I can tell) fine-tuned the "militia purpose" to:

Originally Posted by Justice Scalia

We therefore read Miller to say only that the Second Amendment does not protect those weapons not typically possessed by law-abiding citizens for lawful purposes,

At least one scholar/lawyer has suggested that should include some version of "or would be so, if not banned."

So if you want Peruta to extend to a KA-Bar, or an M9, you'd probably first have to establish the military still uses them- apparently more problematic and disputed than you would think- and that without the ban they would be in common use for a lawful purpose - Probably much easier than one would think because of the same disputation and the source of support for them- THEN convince the court that the ban is the only reason they're not in common use and the protection should be extended to those items not commonly used only because of a ban that would be unconstitutional to apply today if they were in common use in a cause/effect chicken/egg type of game.

The people who do the legal thing for a living can correct anything I got wrong, but having watched this go on for a bit, it's all a step-by-step meticulous process where almost nothing is a gimme. They'll deny a weapon is "arms" and so not protected by the 2A if that gets it off the streets.