Continuing the Sig Brace Saga, the Acting Chief of the ATF released an opinion letter, revoking all other ATF letters on the subject, clarifying the proper use of the Sig Brace as well as how improper use (ie. Shouldering) violates NFA. Read the opinion letter at the link.

http://www.atf.gov/sites/default/files/assets/Firearms/FirearmsIndustry/open_letter_on_the_redesign_of_stabilizing_braces.pdf

-kfg