Originally Posted by MikeJK
If it has a stock it is not a pistol. They make pistol buffer extensions that will not except a stock.
Some make special tubes that won't accept a stock. You can use a regular old buffer tube, but I would find a way to make it soma stock wouldn't fit on it. Unless the stock is on the rifle, it's not a SBR, so you could technically have a pistol AR with a normal buffer tube without having it modified so as to not fit a stock, and have it right next to a stock that's just waiting for a buffer tube, and TECHNICALLY you're still ok. There is no "intent to make an unregistered SBR" charge, but that doesn't mean you won't get hassled and questioned for it. Save yourself the time and either make a normal buffer tube incapable of accepting a stock, or buy a special one. I have seen foam padding on the tube and even a cheek weld piece that attaches to the tube, as long as it isn't a stock (defined as something made to rest against your shoulder) then its ok.
People say all sorts of stupid things, like it's illegal to shoot the rifle with the buffer tube on your shoulder since that would be using it LIKE a stock, but they are full of crap. The buffer tube was designed as part of the rifle, part of how it functions/cycles, with no thought to it being a piece that was intended to rest on your shoulder. It is therefore, by definition, not a stock. They can't tell you HOW you can or cannot shoot your rifle, it would be like telling you it's illegal to fire the rifle with the buffer tube resting on your knee. Just know the definition of a stock, don't ever put one on it, and you should be in the clear.