DTA already spells out in their marketing the difference, go to their website. From a A1 and A2 owner I find that these are also worth knowing: A1 has continuous top rail, A2 has easier to switch handguard. Trigger was the biggest difference between the two. I liked both triggers for different reasons. But I prefer the adjustable A1. Other than that same same...I thought that there would be a bigger difference but I find there are more similarities than different.