Sounds more like a gas assist than a spring assist. Taken from Winchester's website:
"Four massive lugs provide support, strength and solid lockup in the receiver of the lightning-fast Super X® Pump. Under recoil the mass of your body begins to slow the rearward travel of the shotgun, while the inertia of the bolt, slide and forearm continue cycling the action to help you get a head start on your next shot. Dual steel action guide bars channel and eliminate twisting, binding, wasted time and energy when cycling the action."