There's an excellent examination of our previous story on an ATF letter to Black Aces Tactical dealing with whether using a SigTac SB15 brace changes the classification of a firearm.

Over at Prince Law Offices, Adam Kraut takes a detailed look at exactly what Firearms Technology Branch acting chief Max Kingery wrote in his letter and puts his legal mind to the challenge of interpreting it and applying the verbiage to the law.

In short, Kraut admits the letter is worrying, but says people who shoulder the Sig Brace installed on an AR pistol are notionally safe from prosecution under the law.

Is it possible that ATF has now changed its position on the SigTac SB15 arm brace and is getting ready to issue a determination letter which would result in an individual shouldering an AR-15 type pistol with the brace converting the firearm into an illegal short barreled rifle?If so, ATF has apparently chosen to ignore the definitions found in the National Firearms Act again. Attaching the brace to a buffer tube and shouldering it is not “making or remaking” nor is it “designed or redesigned ” from its originally intended purpose. ...

If ATF is planning to issue a determination letter similar in nature as applicable to AR-15 style pistols, ATF will have failed to reconcile that under NFA an AR-15 style pistol cannot be defined as a “firearm” as it doesn’t meet any of the criteria! An AR-15 style pistol was never a rifle and as such even with a SigTac brace attached falls outside of NFA’s regulation.

It's awesome to see a lawyer apply his knowledge of firearms law to the question. And Kraut's analysis is a whole lot more credible than some of the armchair attorneys out there who weighed in as well. Kraut adds that the Black Aces ATF letter may have "opened a Pandora's box" on how the Sig Brace can be used, he says the law is on your side if ATF tries to crack down.