Winchester SX4 Hybrid Hunter FDE/Mossy Oak Bottomland 12ga 3-1/2in Semi Automatic Shotgun - 28in - The SX4 is built on the bulletproof Active Valve system that was the core foundation of the SX3. Building on that solid operating mechanism and improving the balance, controls, and internal operating components of the SX4 to make it a worthy successor to the SX3.