Black River Manufacturing Ported Benelli M4 12 Gauge Shotgun Barrel 18.5 in Chrome Linded OD Green. When the cartridge is fired gases push the shot down the barrel and as it passes each port some gas is vented out to counteract muzzle rise and reduce felt recoil. Black River Manufacturing barrels are drilled from 4140 steel instead of 4130 which has nickel in it which makes it softer. 4130 is used because it can be extruded to make barrels to cut down on costs leaving you with a low quality barrel. Theirs are drilled from 4140 to ensure the highest quality possible. All of Black River Manufacturing barrels come with their extended ported choke which is threaded in Benelli Mobil thread pattern. Specifications for Black River Manufacturing Ported Benelli M4 12 Gauge Shotgun Barrel: Manufacturer: Black River Manufacturing Finish: Chrome Linded Fabric/Material: 4140 Steel Barrel Length: 18.5 in Shell Length: 2 3/4 in Gauge: 12 Gun Make: Benelli Gun Model: Benelli M4 Condition: New Gun Type: Shotgun Package Contents: Black River Manufacturing Ported Benelli M4 12 Gauge Shotgun Barrel Ported extended choke What firearm models does the manufacturer say Black River Manufacturing Ported Benelli M4 12 Gauge Shotgun Barrel is compatible with? The manufacturer suggests that Black River Manufacturing Ported Benelli M4 12 Gauge Shotgun Barrel is compatible with Benelli M4Black River Manufacturing BRBMPBOD: Ported Benelli M4 12 Gauge Shotgun Barrel 18.5 in Chrome Linded OD Green