When the U.S. Marine Corps went shopping for a combat shotgun, they bought a Benelli. That's because a combat shotgun has to function the first time, every time. The Benelli M4 does it for the U.S. military, and now can be the centerpiece of your own home defense plan. Benelli engineers developed and patented a unique auto-regulating gas-operated (ARGO) system. Dual stainless steel, self-cleaning pistons located just ahead of the chamber operate directly against the bolt assembly. It's a simple and dependable system that eliminates the complex linkage, springs and heavy parts that other semi-automatic shotguns have to depend on. The result: Marine-tough reliability under the harshest environmental conditions. The M4 comes standard with a Picatinny rail for optics, a ghost-ring fully adjustable rear sight and fixed blade front sight; a variety of modular stocks are available as accessories. The M4 is combat proven and U.S. Marine Corps approved - why would you depend on anything less?