Can you put a sig brace on a rifle?

Of course. What would make you think you couldn't?

I dunno. Maybe it makes the rifle too short of an overall length. Iv never built one.

Yes, but why would you want to.

You can.

You cannot put a barrel with an OAL of less than 16" no matter what unless it's an SBR or has never been a rifle, ever.

Since ar lowers are sold as "other" on a 4473, exactly how does that hold up as to whether something has or has not ever been a rifle?

Comes down to what the prosecutor can or cannot prove.

Comes down to what ever the BATF agents says your intent was, if he/she tells the prosecutor that your intent was to build an illegal rifle, then that is what they prosecute you on.

Does not mean you are always going to be found guilty but it is going to cost you a hell of a lot of money to prove your innocence.

DEAR SIR please write a letter to the BATF to clarify this...

like was stated earlier, you can. But, why in the world  would you?

Have you ever built it as a rifle?  Then it's always a rifle.

If it's stripped, you can make it into a pistol.

From what I understand, you cannot go back from rifle --> pistol.

Lowers are cheap.  Risking pissing of the .gov is not.  If you want an AR pistol....just buy a new stripped lower that you KNOW has never been a rifle.

Everyone has their idea of what might hold up......but to me.....if there was any question that a lower had ever been built into a rifle, I'd be buying a new stripped lower and going that direction.  It's just not worth it when a stripped lower is less than $100.  Defending yourself from a criminal gun charge will cost you 100x that.  Makes it an easy choice.

It does not work that way all the time. Not all AR lowers are, were or have been sold as other !  It comes down to what was placed on the 4473 at the time of transfer. Because that is the only paper trail as to the configuration at time of transfer.  Configured as transferred to original buyer is where the rubber meats the road. It is a cluster fuck of epic proportions if you look at the realietys of commerce within the firearms industry relating to AR receivers and the technicalities of law. A Reciever that left the factory as other..could have been transferred as dam near anything by a dealer. A Reciever that left the factory as a rifle may have ended up getting stripped and floated around some gun shop for a few years and then sold as a other, pistol...? Right or wrong ? That shit happens all the time. The consumer having no knowledge what so ever. They went to a dealer purchased what they wanted. Dealer wrote some shit on a form. They signed it and walked out. The only place the transferred configuration of a stripped Reciever would show up is on that 4473 from the first dealer that transferred it. Again.. Right or wrong. Many dealers will ask your intention because they want to put Rifle or Pistol on the form. And... Right or wrong. Some dealers just have no clue and made mistakes transferring AR receivers under the wrong configuration. Perfect example as to why the whole thing is nonsense. Original configuration of a Reciever should never come into it. Only what is the current configuration and does it meet the legal definition of pistol, rifle, SBR, AOW, SBS, MG, SBR or DD.
Making the assumption that all stripped receivers you may come in contact with are or were originally transferred or sold as "Other" may very well not be true. Some dealers will not sell a stripped Reciever unless you tell them your intended configuration so they can put it on the 4473.

And legally it doesn't matter if the FFL recorded it as a rifle or pistol in error on the 4473, so long as it was never actually assembled as one, it remains just a receiver.

If first built as a rifle it can never be a pistol, but if first built as a pistol it can go back and forth as often as you wish. Although once its an SBR it can never be a pistol.

Can a dealer legally take a rifle and convert it into a receiver (for example sell the upper and lower of an AR seperatly)?  I know they can't legally assemble an upper and lower and sell it because that makes them a manufacturer.

The above posters are correct.  It doesn't matter what is on the 4473.  The whole thing is bullshit though with a lot of grey areas.

For example:

Is an OEM version like produced by Aero, BCM, Colt and Anderson that ship without furniture a pistol or a rifle? If I were to take a virgin receiver put a 16" barrel on it and a carbine buffer tube it would be a pistol.  My guess though is that they are rifles because that is what the intent of the manufacture was.

For the OP questions, putting a brace on an other wise 16" barreled rifle doesn't turn it into a pistol but is that only in he doesn't intent to fire it with one hand?  Probably a stretch.

What about something like a Cz scorpion carbine.  If I take the stock off for maintenance or cleaning it is less than 26" inches overall with a 16" barrel.  Did I just illegally create a pistol?  What if it had a vertical grip on it, an illegal AOW?  What if it isn't just for maintenance, what if I were to fire it that way as it doesn't need the stock to function.

Who knows what someone at the ATF is going to say one day or the next, I try very hard to follow all the rules.  If they were smart about it and wanted to save work and be more practical they would remove most of AOW's and SBS and SBR's from the registry.  They would loose there two hundred bucks and their registry but accomplish the same thing by creating two categories:  concealable and non concealable firearms.  If it is less than 26" overall or has a barrel less than 16" or 18" for a shotgun it is concealable and you have to be 21 to purchase.  Anything more and you only got to be 18.  Much more practical definition for what they are trying to accomplish but it will never happen.  As my dad always said "Common sense is the least common of the senses."

If an FFL won't sell without you stating your intended use for 4473, then it is time to find another FFL as no matter how the 4473 is filled out, it remains just a receiver until such time as you build it into something.

You can put any stock or brace on your SBR.

When I bought my stripped lower receiver I told my ffl that I wanted it as a pistol.  He said he was told by 2 people at the ATF that he is best to sell it as a receiver.  Since it came to him and went on his book as a receiver then he should sell it as such.  If he transferred it out of his book as a pistol then he could be considered a manufacturer.  The whole system is stupid as stated above.  If the OP put a sig brace on a 16"+ rifle and shouldered it, would that break federal law?  I would bet so but my opinion is worth what you pay for it.

No, because this rifle is still a rifle, despite putting a Sig Brace on it. The ATF issue comes with shouldering a Sig Brace on a "pistol" with a short barrel - thus making that pistol into a short barreled rifle which requires NFA tax to be paid. You can not make a rifle into a pistol by removing the buttstock, it's still a rifle. Likewise, if you have a pistol that meets both the 16" barrel and 26" overall length requirements, you can legally convert it into a rifle by shouldering it, and there is no NFA violation because it is long enough to not require the tax. There is a similar difference with shotguns, but the basic rule is "Once a long gun, ALWAYS a long gun".

OP, in addition to the realization that your rifle can never legally become a pistol, and putting a short barreled upper on it is still making an NFA restricted SBR: You would likely also need to change the buffer tube, because a Sig Brace won't fit over the lug found on carbine buffer tubes (the square shaped part on the bottom that indexes the adjustable stock). It will go onto a pistol buffer tube, or a rifle one, but not a carbine. As for length, with a 16" barrel you only need 10 more inches to stay over the legal minimum 26" overall length. The receiver adds around 7" by itself, and a normal pistol buffer tube adds almost 5", so you should be good. You could run a tape down it to be sure, though.

buy a complete rifle

register an SBR, put a 7.5 inch upper on it

put a pistol buffer and sig brace on it with intent to shoulder it.

you are legal

now take said SBR and shoot in not shouldered and go to jail because you just redesigned your SBR to a pistol and that is illegal because it started out as a rifle.

( this has to be true because if you take a legal AR pistol, put a sig brace on it and shoulder it, you have now redesigned a rifle (SBR) and didnt pay the $200 tax and that is illegal. Therefore going the other way must be true also)

See how stupid these rulings are?

Jesus...

You cannot be prosecuted for "intent".

United States v. Thompson-Center Arms Co.

It is my understanding people have been prosecuted for 'constructive intent'

Is that wrong?

Aren't most conspiracy and terrorist charges mostly intent?

Yes, that's wrong. People have been prosecuted for "constructive possession", not some form of "intent".