I'm looking at getting an AR in the (at least somewhat) near future, and I got a Magpul AFG for it, because my hands fit an AR better with that than they do the stock system or with a VFG. I was wondering if I put it on an AR pistol, would that count as a VFG, and thus make it an NFA firearm, or would it just be part of the handgrip and not an issue?