SX4 left-hand models are the mirror image of the shotgun that rules the skies. The SX4 is based on the bullet proof Active Valve gas operating system that was the core foundation of both the SX3 and SX2. The Active Valve has been tested, tried, and tweaked to perfection to make it the most trusted autoloader in the marsh. In addition to the proven performance of the Active Valve, you get all of the other advantages of the SX4: Better balance, better controls and ultra-reliable internal operating components.