The Benelli M4 was the first gas-operated shotgun that Benelli manufactured. Weighing in at 7.8 pounds, the latest Benelli M4 tactical shotgun fires a 12-gauge round. With a barrel length of 18.5 inches, the Benelli M4 has an overall length of 40.0 inches. Its high degree of maneuverability and its durability are what make the Benelli M4 a popular choice of military and law enforcement members around the world.