So what's the legality of cutting down an adjustable stock to the point that it's only sleave that fits around a buffer tube?

Seems like it would be "redesigned" to no longer be a stock? I know about the Thordsen cover, but I have a Duostock laying around that I'm never going to use, and I'm trying to run the AR with a Vltor A5 buffer tube setup.

I personally don't think it is worth it.  The commercial braces have been deemed legal by BATFE and meet their criteria.  IMHO sell the Duostock and use the money to buy a brace

I would like to.  I think a cut down stock would be a lot more durable than the CAA saddle.  

I haven't because it's easy to build something illegal, or at least something that may look illegal to someone.

The thing I keep thinking about is even if you cut it down, there is still at least a small part that was originally meant to be shouldered.  You've essentially just created a small buttstock.

The BATF doesnt want people shouldering pistols. If you never shoulder it, and maybe remove the butt pad entirely to make it clear that it is just a protective cover, you may be OK. See the batf letters on using a rubber end cap on the buffer tube and shouldering the sig arm brace. According to the atf it is very easy to "make" an sbr

I bought a rubber cover for buffer tube and it works much better than touching that cold buffer tube.  I have the braces as well, but this lower has pistol tube, so I went with what I already had.  Rubber cover works pretty well.

How would it be any different from altering a rifle stock into a mares leg for use on a pistol? Why is one kosher, but chopping an AR stock seems like it rustles a lot of jimmies.

Because BATFE. Oh, and braces being shown on YouTube as stocks and idiots writing letters to ATF asking "are you sure this is legal? "

 

Esp since now the doctrine is whether you shoulder it or not makes it a stock I am sure that cutting the butt plate and the
Buttress off an M4 stock to use as a cheek rest is justifiable, especially if you fix it in position so that the back of the reciever extension is poking out the back.   But, you might be made to justify that before a grand jury, if however unlikely.  

I thought about doing just that since I need an elevated cheek rest, but I will just buy the Thorsten and use the snap on CAA risers rather than modding a stock I guess.  It is better to having something that was approved to that purpose to begin with, sort of like using a pistol marked loser, not technically required but could save you from having to prove your innocence.