The original Armalite of Fairchild Aircraft Corp AR10 waffle mag developed by Eugene Stoner in the 1960's is the same functionally as used by Knights Armament in their SR-25, DPMS LR-308, and is interchangeable with the .308 PMAG.
The current Armalite of Geneseo, IL has two lower receiver variants, one takes a modified M14 magazine and the newest accepts the original AR10 waffle type that works in Knights, DPMS LR-308 and others.
The reason Armalite of Geneseo, IL went with the modified M14 mag was due to the ban and they took existing mags and modified them to be used in their AR-10 as no new high cap mags could be manufactured for civilian use and it was also a proven design.