The A400 is built by using a recoil reduction technique that provides greater recoil administration when compared to the A300. I such as the SX4 at the same time, but I really need to say, I favor the A300 Ultima. The Widened loading port and adjustability give it the edge. https://beretta-a300-ultima-vs-a469000.thezenweb.com/the-5-second-trick-for-beretta-a300-vs-a400-64527516