Was considering SBRing my GSG-5P, turning a "pistol" into an SBR for $200 tax stamp. Afterwards, can I add a vertical foregrip without turning it into an AOW and having to pay another $200 tax stamp? Really only wanted the grip but since I was thinking about SBR anyway makes no sense to do it in the "wrong order" if it is going to cost twice as much. Who wrote these laws anyway?