Later this year once other priorities are funded, I’ll be acquiring a 9mm AR upper (the BRN-9) which works with my AR-9 lower. The design of the BRN-9 contains the recoil spring and blowback mass in the upper, so I can remove the buffer tube.

The intent is to minimize size and weight for a PDW/bag gun build.

I was originally thinking a LAW Folder, but since I don’t need a buffer tube at all, are there any other, more radical collapsing stocks out there which would take up even less space?

I was wondering if something like this existed for normal ARs; no buffer tube and a wire stock that collapses around the receiver, though this one seems specific to the SIG MPX or MCX: https://www.sigsauer.com/collapsing-telescoping-stock-mcx-mpx.html

There are a lot of AR-15 9mm PDW stocks, but they use a very short buffer & tube.

Have a look at AR-15 buffer tube picatinny adapters. Maybe that will let you use any picatinny mounted stock or even a CZ Scorpion stock.

A3 Tactical makes a “universal” PDW style stock.  I’ll see if I can dig up a link.

ETA:

Stock:  https://a3tactical.com/modular-telescoping-stock-universal-picatinny-1913-mount/

Pic Adapter:  https://a3tactical.com/rear-brace-stock-adapter-ar-buffer-thread-to-picatinny-1913/

You could also pick up basically any MCX compatible folding stock with a folding hinge.  Without the buffer tube, they collapse a lot more flat than the LAW folder setup.

Good to know, thanks! I didn’t know the MCX stock was about half as thin as a Magpul CTR and LAW Folder, so I may just go down that path, but I also like that collapsing stock design; it is exactly what I asked for.