The Benelli M4 H2O is a semi-automatic 12-gauge shotgun with an 18.5-inch barrel and a corrosion-resistant H2O finish. 
 

Key Specifications 

• Model: M4 H2O 
• Manufacturer: Benelli 
• Caliber: 12 Gauge 
• Action Type: Semi-Automatic 
• Barrel Length: 18.5 inches 
• Overall Length: 40 inches 
• Weight: 7.8 lbs 
• Magazine Capacity: 5+1 rounds (accepts 2-3/4" and 3" shells) 
• Choke Type: Modified (M) 
• Sights Type: Ghost Ring 
• Grip Material: Polymer 
• Stock Material: Synthetic 
• Recoil System: Heavy 
• Safety Feature: Yes 
   

Detailed Features 

 
The H2O finish is a corrosion-resistant coating suited for maritime or high-humidity environments. Ghost ring sights give quick target acquisition without an optic. A Picatinny rail on the receiver lets you mount lights or a red dot if needed. The gas-operated ARGO system cycles a wide range of 12-gauge loads reliably. The synthetic stock is fixed rather than adjustable.

The M4 H2O draws consistent praise for its reliability, particularly the ARGO gas system's ability to cycle varied loads without issue. The corrosion-resistant finish is a frequent highlight, especially from owners who use the shotgun in wet environments or store it in humid conditions.

Ergonomics get generally positive marks: the weight distribution and grip geometry work well for fast handling. Recoil is described as manageable by most owners. Price is the main friction point, as the M4 platform sits at the high end of the tactical shotgun market, and discussions regularly weigh whether the premium over more affordable options is justified. Customer service experiences with Benelli are mostly positive.