BREAKING: ATF Confirms Firing an AR-15 Pistol From the Shoulder Using SIG's Brace is A-OK - The Truth About Guns looks like it is ok... I would cross verify with a second source...
Like the opinion of strangers on the interwebz ? If I were to have a SBR or SBS in my possession whilst out and about I'd have a copy of a (Form 4) either on my person or in the stock of the firearm for provenance. If I were to carry an AR pistol equipped with this brace I'd want a letter from the BATFE addressed to me carried in a similar manner.
A friend of mine has copies of his NFA transfer and stamp shrunk to the size of a business card and laminated so he can take them with him when shooting or transporting while the real paperwork stays at home.
I was surprised how readable it was. I would do the same for mine, but I'm going to sell it to fund other things. For me semi-auto is the best choice so it no longer makes sense to keep the money tied up there.
Nope, not legal* and it hasn't been since January 16, 2015. I can't post links because I just registered, but try googling "shoulder sig brace". Even better if you can filter out anything written before 1/16/2015. atf (dot) gov/file/11816/download *Many people argue that the ATF doesn't have the authority to make new laws, and therefore it is still legal to shoulder the brace. They don't have the authority to make laws, but they have authority to interpret & enforcethem. Unless their interpretation gets struck down in court, it is de-facto law.
Technically, by the same argument it be unlawful to shoulder the pistol using the buffer tube. If you get jacked up for either, they're looking for a reason to do so.