From The Manufacturer/Wikipedia/People Smarter Than Us:
On the surface, the AR-30A1 bears a family resemblance to its predecessor, the AR-30. But, every individual component of the AR-30 was scrutinized in the AR-30A1. As a result, only the pistol grip, buttpad, trigger, and a few small components from the AR-30 passed muster for the AR-30A1.