Eventually I'd like to buy a short 300 Blackout upper and make it a pistol. If legal, I'd like to be able to just slide the stock all the way off my buffer tube and use the same lower, only putting the stock back on after swapping to a 16-inch upper.

A quick web search gives me results that don't exactly match what I'm asking. Is it ok for me to just pull the stock off when building a pistol, or do I legally need to use a round buffer tube that you are unable to put stocks on?

You need to have a legal use for that stock body. Simply removing the stock body from the tube doesn't cover you if you retain the stock body and have no other use for it than to go back onto the telestock buffer tube on your "pistol" build.

So no, you don't have to have a "pistol buffer tube", but you do need a legal use for the parts in your possession. Have another stripped lower around, or a rifle that stock body can mount to, or get rid of the stock body until your stamp comes in or you get another lower to which it could theoretically be mounted.

Yes you can do that but it needs to be a pistol first.

So I have to do it with a separate lower that is only used for pistol builds, and having an extra stock around could be used as evidence of intent to build an unregistered SBR? Do I have that right?

You just need a virgin lower, which is one that has never had an upper attached. It doesn't matter if it comes with a stock installed when you buy it, so long as the stock is removed and a pistol length upper is the first thin attached to it then it will become forever a pistol lower. And then you can remove the short upper, install a rifle length upper, and attach the stock when you want to convert it temporarily to a rifle.

I would just use a pistol buffer tube for the time being

The lower has to have never been a barreled rifle.

Then you can make it a pistol.

there is no reason why you can not have spare parts for other guns you have or parts that will allow you to build a new rifle.

on the other hand it is cheaper to have a $50 pistol buffer than running into LEO that does not understand the law.

Stupid laws meant to entrap the innocent.

Virgin lower made in to a pistol first, will always be a pistol lower.

Write a letter to the ATF.

This is what you need to do.

Buy stripped lower.

Build it with standard buffer tube and no stock.

Install short upper.

Its now a pistol.

You can now swap to a 16" upper and add a stock. It is now a rifle. Take stock and 16" upper off, install short upper it is again a pistol.

Point being you cant take your stocked 16" rifle and remove the stock and install short upper. That receiver cannot have begun its life as a rifle. It must have started as a pistol.

So pistol to rifle to pistol to rifle is fine.

Rifle to pistol is a no go any way you slice it.

As crazy as it sounds, this is how I understand the ridiculous law too.

Buy a pistol tube. I paid $30 for one. Also buy a striped lower and keep the original box. Problem you are most likely to encounter would be with local LE so having black and White answers to their questions is better than having to defend gray area answers. That's why I went ahead and SBRed my pistol when ATF made braces a gray area. 

there used to be an archived ATF letter stating that any buffer tube was acceptable on a "pistol"... as others have commented, make it from a virgin lower identified as "other" on the 4473...

Short answer, no, you can't do what you just told us was an illegal conversion.

There is also the real world case of a fireman who was carrying both an AR rifle and a pistol broken down in the same case, who left it in his vehicle, which was searched and siezed by the cops (for safekeeping as the vehicle was getting towed) who then put the weapons bag in the evidence room where police assembled it into an illegal configuration, sending photos of it to the ATF, who then prosecuted him. He lost because of a bad lawyer and last I heard is still appealing it.

All because of some rivalry with the cops. One in ten thousand odds or even worse, but there it is. Which is why so many of us just build a separate pistol with pistol buffer tube and separate carbine.

These things are so dirt cheap right now giving up an expensive phone plan and spending the dough on parts will build you both in one year. Think about it. I have a PAYG minutes phone that costs me less than $100 a year - not $100 a month - that leaves $900 on the table. You can buy completed AR15's under $400 now. I did it when either would cost you over $650.

It's a fantasy to think you will swap them around anyway, each has its specific application and as you push them toward their best configuration it pretty much voids using it the other way. A pistol lower isn't a good foundation for a good overall rifle - compromise sets in and you find yourself limited in things like grips, triggers, mag releases, ambi controls, etc as the best for one eliminates the best for the other in a lot of situations.

Goof up the assembly process at a range in public and you may well have some idiot take a pic of your mistake to your very considerable regret. Not having that happen and making sure of it is much safer - plus you get two working guns instead of a bunch of leftover parts not earning their keep and being a risk factor.

It boils down to just because you can doesn't mean you should. And the track record of the ATF also means it's only a temporary situation, things can very well change again. At one point a pistol could have a stock on it pinned to the shortest length, but not now. All those pistols had to be reworked at the owners expense.

Misread post

I just keep a pistol configured lower in my safe all the time, pick up a cheap stripped lower and pick up a PSA pistol builders kit, put together put in the safe and you have covered your ass.

http://palmettostatearmory.com/psa-pistol-lower-build-kit-black.html

This.

One of his friends posted on here the other day he was serving 30 months in the Fed Pen.

Yes,  buffer tube needs to be modified so it is impossible to afix a stock to it.

While many feel this is a safe precaution to take, I have yet to see it in writing as a Legal Requirement.

Really?

That is not wrote into the regulations anywhere, that is a misconception.

Now if you can find a regulation to that, please post a link to it..

If you're really interested in keeping the standard tube get a Thordsen brace/saddle. It uses the standard extension.

I use one on one of my pistols its pretty nice.

False

Seems all the regs I've seen and the commentary from most of the fairly knowledgeable folks on this site support that you can use a bare carbine extension tube on an AR pistol.  I think it would have to be a chain of almost inconceivable circumstances on the part of a gun owner to get himself jammed up on a federal charge involving an SBR violation in this scenario.  That fireman situation is often cited here, but you just gotta think there was more to that story for some reason.  I can see in a silly situation where you're running around with a bag of unattached carbine buttstocks...and your pistol with the carbine extension...and no rifle/legal SBR anywhere in the area to attach those buttstocks...well...you might actually get a violation or at least heavy duty scrutiny from BATFE.  Still, most of the times any of these issues get a federal light cast upon them is when the gun owner is doing something else unadvised that gets the attention of law enforcement.  The best advice anytime you're around any of your personal weapons in public...behave.

Funny thing...an AR pistol with just a naked carbine extension tube is probably the absolute best and true argument about classifying it as a pistol as it might be easier to convince someone how sticking that sharp edged, hard carbine tube into your shoulder would really suck.  OK...I joke.

I used a carbine tube on my first pistol build, I filled in the stock indentation holes with clear silicon caulk then put a pistol tube cover on it. The $8 ones from Amazon that are closed on the end. Tight fit, but it fits.

This is what happens when bureaucrats that know nothing about guns make the laws, you get stupid asinine stuff like this.

OP you have a rifle, it can never be a pistol.

OP you need to buy a virgin lower, build it or buy one built then attach the short upper making it a pistol, then you can swap back and forth as much as your heart desires.

Did the cops make it home safe?

Get one of them new fangled braces that you can legally shoulder until you get your stamp back so you can add the stock and legally shoulder it.

That is imperative!

The simplest solution to all this is instead of all the hand wringing about converting from pistol to rifle, just get a second lower to out the 16" upper on. Then you don't have to swap uppers back and forth every time you want to shoot a rifle length barrel.