I am looking for something that may or may not exist

[Hirschkopf]

I'm a fan of the Springfield Armory Saint Edge PDW. Here's a review and some details on how they put it together; maybe some of it could be inspiration for your project:

Springfield Saint Edge PDW AR Pistol Review - Guns and Ammo

The Springfield Saint Edge PDW conceals and transports incredibly well, is surprisingly soft-shooting, accurate and reliable, unique and fun.

www.gunsandammo.com

 

[bushmaster06]

Stock options are limited as most will use the buffer tube for support. So you can use a shorter buffer tube using the DFA option listed below, and there are seveal others. You can also go MPX stock and and a picatinny adapter that replaces the buffer tube. You can then use a BRN180, JKL upper or any short barreled piston driven upper like the Adams Arms. LAW Tactical makes a modified bolt that lets you run any upper you want with no buffer. Evolution Systems does too but its backordered.

KNS AR-15 Buffer to Picatinny Rail Adapter Kit Flange

The KNS Precision AR/MCX Stock Adapter allows the user to mount a picatinny-style stock attachment (such as the SIG MPX folding stock or brace) in place...

www.midwayusa.com

MPX/MCX Stabilizer

Introducing the Strike Stabilizer for SIG MPX/MCX. Improve your pistol’s ergonomics and utility by combining the MPX/MCX mounting system and the Strike Industries patent-pending stabilizer design. Designed to work with the existing receiver cuts, the Stabilizer collapses to an extremely compact...

www.strikeindustries.com

DFA MCS - AR-Pistol Kit 2.5"

The DFA Modified Cycle System for your 9MM AR! Our MCS significantly shortens your AR profile while maintaining the quality needed for repeated fire.

deadfootarms.com

Uppers and bolts

Adams Arms AR-15 P2 Adjustable Gas Piston Pistol Upper Receiver

This Adams Arms P2 Adjustable Gas Piston Upper Assembly is chambered in 5.56x45mm NATO and comes ready to fire right out of the box after installation...

www.midwayusa.com

Law Tactical ARIC

Fire folded repeatedly with the Law Tactical ARIC (AR Internal Carrier) The ARIC replaces the Complete Bolt Carrier Group and Recoil System of standard AR15 style firearms. ARIC (AR Internal Carrier) is designed to drop into your host firearm with the LAW Tactical Folder Stock Adapter (FSA).

www.lawtactical.com

I think it was Brownell’s that I got a pistol buffer tube from that was the outside diameter the whole length of the tube so I could cut it shorter and run a threading die. I’ll upload a picture later.

 

[OKNewshawk]

Dead Foot Arms is what you want. They make a 2.5 in modified cycling system buffer that you can put a SCW extendable stock or brace on it. If you are a veteran, you can also get a lifetime 10% discount after verifying your veteran status. SCW25-STOCK-RC-GEN2

 

[bushmaster06]

Here’s my SB Tactical that I modified. I could probably cut the tube down another 1/4” and you could probably cut the part that supports the bars shorter if you wanted, but it might sacrifice stability of said bars. I also cut more notches in the bars for they collapse further in.

I think if paired with a piston upper or the special BCG you could chop the tube really short.

 

[bushmaster06]

@kingfish