Exactly.
> Adjustable stocks are arguably a concern because they make building rifles shorter than 26 inches easier.
You could just not put stock on. An AR-15 with a 16in barrel is 30in with the stock collapsed and cannot be much shorter without the stock because of the buffer tube.
Telescoping stocks maybe not (my inexperience showing there) but folding stocks definitely can take it under 30 inches then. I assume you're saying a normal caliber ar15 won't be very fireable without a buffer tube. Anyways, apparently folding and telescoping stocks are also illegal in California, which might be the real reason amazon has these rules.
They are not illegal to own in California. They are only illegal to be on a semi-automatic center fire rifle with a detachable magazine. So if you mag lock your AR with something like this[1] you can put a telescoping stock on it. This is also legal[2] (with a 10rd magazine) since it is not a center fire rifle.
Again a stock is not integral to the operation of most rifles so you can just not put one on. Oh course then it's legally not considered a rifle most of the time.
>Rimfire ammo is limited to smaller calibers since the cartridge walls need to be thin enough to be able to be crushed by the firing pin and ignite the primer.
> The downside?
> Well, the nature of the casing means it’s pretty much limited to small calibers. You have to have some relatively flimsy brass to handle the rimfire set up. As a result, the powder necessary to propel a larger bullet would blow the brass apart.[1]
Correct about the buffer tube. So even if you installed a folding stock on an AR-15, it require some proprietary buffer tube to work like this one.[2]
[1] https://www.pewpewtactical.com/rimfire-vs-centerfire-ammunit...