This may be a total Noob question, but at what point does a buffer tube become a stock in the eyes of the ATFE?  Looking at some pics of these AR pistols, I think I could shoulder some of those buffer tubes for stock-like stability (sure it's not comfy, but hey, CQB is pretty un-comfy anyway).  With an EOTech or such in place, you'd have a functional SBR sized package without the SBR paperwork.  Thoughts?

I'd use the search feature.  There have been many threads concerning this question.

A stock is something that is made and designed to be shouldered. A buffer tube is not designed or made to be shouldered and therefore is not a stock.  Doesn't matter what else you use it for, it is not a stock.  

As was said, a buffer tube is a buffer tube, a stock is a stock.  The buffer tube becomes a stock when a stock is put on the buffer tube.  Do the search suggested as this has been gone over about a hundred times, at least once per page for months.  Also see the letter regarding this topic that I have posted lots of time in most longer pistol threads.  See the AR pistol thread in the General AR discussion forum.  

As long as there are no threads or other provisions to mount a stock or stock components (in other words a bare tube) then it isn't a tube.

The buffer tube becomes a stock when a stock is put on the buffer tube.

Dont' forget about mere possession of the remaining stock piece.  

Parts on hand = constructional intent = SBR = AFT related migrane!

Quoted: The buffer tube becomes a stock when a stock is put on the buffer tube.   Dont' forget about mere possession of the remaining stock piece.   Parts on hand = constructional intent = SBR = AFT related migrane!

Your pistol upper fits your rifle lower, so that's constructive intent as well.
It could happen.

This whole "constructive intent" thing still makes little sense to me...

IF you went through the whole ATF process, why would they assume you would instantly
make an illegal weapon?

I have beer in the fridge, I own a truck,  
Why aren't I arrested for "intent to drive drunk"?

ARGHHHHH  Not this crap again.
Contructive intent only applies if you own the butt stock and ONLY the AR pistol and when the ONLY way those parts can be assembled in into an illegal SBR.  The ONLY way, not "in a way."  So long as you own an AR rifle or a rifle upper, you can own the butt stock, or two, or three.  And it is not a NFA weapon so please don't bring out those NFA letters again.  TC court ruling, so long as you do not put the butt stock on when the pistol barrel is attached you are legal so long as you own a rifle upper in addition to the butt stock.  And it doesn't matter squat if the tube can take a butt stock or not.  Damn, how many times does that freaking letter have to be posted.

Quoted: ARGHHHHH  Not this crap again. Contructive intent only applies if you own the butt stock and ONLY the AR pistol and when the ONLY way those parts can be assembled in into an illegal SBR.  The ONLY way, not "in a way."  So long as you own an AR rifle or a rifle upper, you can own the butt stock, or two, or three.  And it is not a NFA weapon so please don't bring out those NFA letters again.  TC court ruling, so long as you do not put the butt stock on when the pistol barrel is attached you are legal so long as you own a rifle upper in addition to the butt stock.  And it doesn't matter squat if the tube can take a butt stock or not.  Damn, how many times does that freaking letter have to be posted.

This is correct, the other junk about "constructive intent" is WRONG.

Quoted: Quoted: ARGHHHHH  Not this crap again. Contructive intent only applies if you own the butt stock and ONLY the AR pistol and when the ONLY way those parts can be assembled in into an illegal SBR.  The ONLY way, not "in a way."  So long as you own an AR rifle or a rifle upper, you can own the butt stock, or two, or three.  And it is not a NFA weapon so please don't bring out those NFA letters again.  TC court ruling, so long as you do not put the butt stock on when the pistol barrel is attached you are legal so long as you own a rifle upper in addition to the butt stock.  And it doesn't matter squat if the tube can take a butt stock or not.  Damn, how many times does that freaking letter have to be posted. This is correct, the other junk about "constructive intent" is WRONG.

+1

Constructive intent is BS 99.9% of the time.  A plumber that also does reloading has powder, pipe and end caps, does this make "contructive intent" for a pipe bomb?  I have a shotgun and a hack saw is that "constructive intent" NO.  

Now I would think having all the M16 FCG parts and an AR15 without having a legal M16, I would call "constructive intent".  That is the only time I could see "construction intent".

Quoted: Damn, how many times does that freaking letter have to be posted.

The letter should be  thumbtacked and then closed off so no nonsense can detract from it.