I I have both and the TAC 21 is by far a superior design the ax chassis the action sits in top so you get a lot more barrel rise where the TAC 21 is a in line set up like a AR has so the barrel does not rise like in a conventional design and it also has a much different recoil impulse that is much softer and as far as ergonomics it is much more comfortable to shoot to me than the AX chassis is and it uses the AI mag so you have the best of both worlds, I liked the TAC 21 so much I have three of them 223,308 and 300 Norma magam and I am an active duty LE sniper and the TAC 21 is my Duty Rifle