The word is getting around in certain circles of the gunternet sphere. The ATF has made their decision, it is said, that braced firearms are going to be scored per the rule 2021R-08 on a form 4999.
I’ll give you the short version. You have an SBR. Nothing about the criteria listed on the 4999 is designed to make however you are, probably, using any braced pistol style of firearm an SBR. Most of the most common, most aesthetic, and most comfortable brace designs will add somewhere between 2 and 6 points to the allowable total of 4 making it a “Stock” in effect.
We’ve known they were after this determination since SIG first brought the brace fully to the forefront of AR pistol designs. It was a delightful time where we honored the letter of the law but got we wanted too. Unfortunately it sounds like it is coming to an end.
NOTE: I have not seen any official ATF letterhead giving a date or the final terms.
This does not make braces illegal, which is a very clever way to not repeat the disaster that the bumpstock ban kicked off, it makes braces into stocks by use. It scores the brace itself, its attachment to the firearm, and then the other attachments on the firearm, to determine whether or not it is a stock… and therefore the former pistol is now an SBR.
The link above (and here) has the 4999 score sheet. Remember, you cannot break 4 points in any category and some of them are a little… vague still.
Most people running a carbine pistol type of any sort are almost certainly in violation using any of the common… well… anythings. There is no practical way someone is running a non-violating pistol, unless they messed up by the numbers on every pick of every accessory.
They can’t make them illegal to shoulder. Making braces illegal is a disaster. So they have settled on putting together individual pistols in an SBR like way being the problem.
Again, I haven’t seen this in official print yet.