but to answer you question, high level
1) New gas relief spring valve system
2) 5 coil spring instead of 4
3) self cleaning piston, similar design to xtrema 2
4) receiver ligher and shorter, better handling
5) Thicker and heavier bolt assembly A400 Xtreme Gas cylinder collar NOTE: Lighter bolt assembly—rear of bolt cut-out (shaped) differently. Aids in better cycling with wide range of 12 Ga ammo types VS A400 Xtreme Bolt Assembly
6)A400 Xtreme Trigger Plate Assembly More Compact and redesigned
7) Xtrema 2 Standard Screw on Mag Cap A400 Xtreme (B-Lok) quick removal Mag Cap= Fast and Easy Disassembly!
8) A400 Xtreme NEW Kick Off Mega 70% recoil reduction with the NEW Kick-Off Mega system
9)Superior Corrosion protection with AQUA ™ Technology
Phew.................. oh and they have a POD- google it, cool feature, probably more so for the a400 trap and shoot guns, not so much the xtreme
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