In the interest of not being ignorant (I was under the impression that an AR originally configured as a pistol, could be legally configured to a rifle and back without any problems or restrictions), I looked on the BATFE site and all I could find was this page:
with this comment (among others):
Held further, a firearm, as defined by 26 U.S.C. 5845(a)(3) and (a)(4), is not made when a pistol is attached to a part or parts designed to convert the pistol into a rifle with a barrel of 16 inches or more in length, and the parts are later unassembled in a configuration not regulated under the NFA (e.g., as a pistol).
While this quote doesn't expressly address the situation, they discuss the reconversion to a pistol as though it is not an issue at all. The same page does state specifically that you CANNOT make a pistol from a firearm that was originally configured as a rifle ...
I would really appreciate it if you could please post a link to the passage where they clearly state that once it becomes a rifle it cannot be reconverted to the pistol configuration.
Thanks in advance!