Using the 1903 inertia operating design of Danish gunsmith Christer Sjörgren, the Benelli relies on the recoil forces of the fired shell to operate its action. With very few moving parts, these are rugged and reliable shotguns that can shoot shells from light target to 3 ½-inch magnums without adjustment. When the gun is fired, a carefully calibrated spring holds the bolt head tightly in the battery until the gun stops recoiling, then it unlatches the action and the stored inertia cycles the gun while leaving little firing residue in the action, making for easy maintenance.  It's also a very good deer hunting gun.