I'm familiar with mag locking and all of the "featureless" difficulties, I was just being brief. However I understand center fire refers to the cartridge/primer configuration and I'm not really sure why that matters, could I trouble you to explain? WRT the buffer tube, I understand that you need the buffer to move the bcg, correct?

Sure. It matters, I'm guessing because the design prohibits larger calibers due to the physics of how it works.

>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...

[2] https://youtu.be/_qr2GTq3v3w

Oh, that makes a lot of sense. Thank you for your time and knowledge.

You're welcome.

Moreover, having a rifle shorter than 26in is also a federal crime. You might as well go all the way and saw the barrel in half too if you really want a SBR.