The ATF definition of a handgun isn't what actually counts from a legal perspective- what counts is the designation of the firearm itself. If the AR lower is designated as a pistol receiver, then it is indeed legally a pistol and therefore no VFG may be used. (I am aware that there may be no designation to homebrew AR lowers as either pistol or rifle until the firearm is transferred from the maker, and it could be an interesting discussion as to whether the VFG was in fact illegally attached, but one I would likely get paid to have with a prosecutor or jury should someone decide to put a VFG on a short-barrelled AR with a Sig-brace and get burned by law enforcement.)Except an AR pistol is not a 'handgun' by the ATF definition, it is a 'firearm', as the original design was not for one hand operation.
That said, I don't even have an AFG on my AR pistol and the ATF could change it's determination without notice.


