I actually looked into this slightly for about a week. Some variant of the AR pistol is on the handgun roster, but it is restricted and only available for military and law enforcement sale (i.e., no civilian sales).
Engage in Rockville tried to get an AR pistol put on the handgun roster but it was denied.
I'd be interested in knowing whether anybody has bought a AR or AK SBR since October 1, 2013 and how it was handled.
An AR pistol is not an SBR.
I know of several folks that have purchased an SBR'd rifle on a form 4 and the paperwork had it classified as a rifle, not a handgun. MSP signed off on the form 4 and they are currently in the 9 month waiting que for approval from BATFE.