For Lightning-Fast 20-Round Reloads & Ridiculous Reliability, the Mossberg 590M Is a Top Choice

When it comes to competition, tactical or home defense purposes, reliability is king, and ammunition capacity is a close second. Unless the rules of the competition or regulations prohibit, the more rounds on tap, the better. After that comes the ability to make a rapid reload.

Many types of rifles and pistols have had high-capacity magazines for years; shotguns have not. Most domestic shotguns, whether semi-auto or pump action, are limited in capacity to how many can be fit into their tubular magazine, usually four to nine rounds.

The Mossberg 590M is ready to roll.

If an extended magazine tube is installed, the capacity can be increased by anywhere from one to eight rounds, if you can tolerate the magazine tube extending beyond the end of the barrel. The problem then becomes how to quickly reload that tubular magazine. With a lot of practice, this can be done quickly by loading two at a time with up to four in hand. Unfortunately, few of us will ever truly master this process. Most of us will find slapping in a new magazine much quicker.

Some manufacturers, especially foreign ones, make box magazine-fed shotguns with single-stack or drum magazines, but they haven’t become mainstream, and many suffer from reliability problems.

Enter the Mossberg 590M and Remington 870DM box magazine-fed shotguns in 2018. The two share some similarities, but with its double-stack magazine, the Mossberg definitely comes out on top in the capacity category.


The Mossberg 590M is a box magazine-fed pump action 12-gauge shotgun based upon the 500/590 family of shotguns. These shotguns use a twin bar-slide action and are well known for their reliability. The 590M’s claim to fame is its robust standard 10-round double-stack box magazine. Five-, 15- and 20-round double-stack magazines are also available. With this firepower available, score one for the 590M.

 Mossberg 590M Heat Shield


After removing the ghost ring rear sight and installing a baseplate on the drilled and tapped receiver, a Holosun HS-510C reflex circle dot optic was installed.


  • Compact, interchangeable high-capacity magazines (5, 10, 15 and 20 rounds)
  • Mossberg 590 dependability
  • Bi-Lateral magazine release
  • Ghost ring rear and post front sights

Factory Specifications

  • Manufacturer: O.F. Mossberg & Sons, Inc.
  • Website: Mossberg.com
  • Model: 590M Heat Shield (evaluated)
  • Item Number:  50206
  • Caliber:  12 gauge, 2 3/4 inch
  • Magazine Capacity: 5, 10, 15 or 20 rounds
  • Action Type: Pump with twin action bars
  • Barrel: 18.5-inch blued steel
  • Choke: Cylinder bore choke tube supplied; compatible with the Accu-Choke system
  • Forend: Black polymer “corn cobb” style; steel-heat shield
  • Receiver: Aluminum, black anodized
  • Rifling: Smooth bore
  • Rail Mount: Accessory rail available for mounting an optic
  • Sights: Fully adjustable rear ghost ring and front post with florescent orange insert
  • Trigger Pull: 8 pounds 3 ounces, as tested (average of 10 consecutive pulls using a digital Lyman Trigger Pull Gauge)
  • Stock: Black synthetic (compatible with Flex system buttstocks (with adapter))
  • Overall Length: 39.5 inches
  • Weight: 6 pounds 15 ounces (8 pounds 3 ounces with empty 10-round magazine)
  • MSRP: $801

Inside the Holosun HS510C Reflex Optic

The HS510C open reflex circle dot sight features dual power supplies with solar power during daylight usage and battery backup during low light conditions.


Due to its open-frame design, the HS510C offers a wide field of view for better situational awareness. It also is parallax-free and has unlimited eye relief.

The reticle can be switched between a 65 MOA circle with 2 MOA dot, a 2 MOA dot only and a 65 MOA ring only using a single button.

There are 10 daylight and two night vision illumination settings that can be selected by using the +/- buttons. This model uses a red reticle but a version with a green reticle is also available.

A quick detach mount is standard.

Light Source:                                 LED
Magnification:                               1x
Multi-Coatings:                             Yes
Battery Type:                                 CR2032
Battery Life:                                   Up to 50,000 hours
Housing Material:                         6061 aluminum with Titanium hood
Housing Color:                              Black
Adjustment per Click:                   0.5 MOA
Windage & Elevation Travel:       +/- 50 MOA
Working Temperature:                 -22 to 140 degrees Fahrenheit
Window Size:                                 0.91 in.x1.2 in.
Size:                                                3.3×1.6×1.8  inches
Weight:                                          7.6 ounces (actual)


To read the entire review, pick up a copy of the November-December issue.