I know there's been a lot of speculation about this lately. The ATF has made a determination about all those pseudo-SBR's out there.
Per the ATF Firearms Technology Branch:
http://www.thetruthaboutguns.com/20...atf-confirms-firing-ar-15-pistol-shoulder-ok/
Per the ATF Firearms Technology Branch:
FTB classifies weapons based on their physical design characteristics. While the usage/functionality of the weapon does influence the intended design, it is not the sole criteria for determining the classification of a weapon. Generally speaking, we do not classify weapons based on how an individual uses a weapon.
http://www.thetruthaboutguns.com/20...atf-confirms-firing-ar-15-pistol-shoulder-ok/