I just watched a program on the Military Channel about the use of shotguns. The Benelli M4 was one of them.
I copied the following from Benelli's web site:
"Now the same Benelli M4 used by the U.S. Marine Corps can be your home defense shotgun of choice. When the U.S. Marine Corps went shopping for a shotgun, they bought the M4 — the 12-gauge shotgun that functions the first time, every time. Its unique Auto Regulating Gas Operated (A.R.G.O.) system developed by Benelli engineers has dual stainless steel, self-cleaning pistons located just ahead of the chamber that operate directly against the bolt assembly.
The M4 Tactical comes standard with a Picatinny rail for optics, a fully adjustable ghost-ring rear sight and fixed-blade front sight and a black synthetic pistol-grip style stock. An optional standard stock is offered. With features and reliability that do it for the U.S. military, the Benelli M4 is an excellent choice for your own home defense plan."
I think that, if you are considering a semi-auto shotgun for defensive use, you may want to check this one out. And, if you get the Military Channel, keep an eye out for their test of this gun. It looks good to me.