May 24, 2022

M27 IAR vs M249 SAW – Full Auto Fun

The Marine Corps made waves when they announced they wished to replace the M249 SAW with an automatic rifle. The concept of an automatic rifle had been used extensively. In WW1, weapons like the Chauchat occupied the role. Later, the BAR became the automatic rifle of choice. In Vietnam, the Stoner 63 configuration was tested in the automatic rifle variant, and after Vietnam, the Marines used a modified M16A1 with bipods as an automatic rifle role. The M27 IAR isn’t your normal piece of AR15 Kit though. It’s a piston driven monster

The M249 SAW represented one of the first true lightweight, 5.56 caliber, belt-fed machine guns. It gave a rifle squad three machine guns that gave a rifle squad overwhelming firepower. The M249 served well in the Global War on Terror, but the Marine Corps wanted to move forward with the M27 IAR. It’s still a contentious move and an interesting debate.

Suppression Theories and Debate

Traditionally suppression was done through overwhelming firepower. A belt-fed SAW feeding from 100 or 200 round belts allowed a squad to provide overwhelming organic firepower on the enemy. The M249 and machine guns, in general, are not generally efficient weapons for killing the enemy. They spray a volume of fire that’s designed to keep an enemy pinned down.

With an enemy pinned down by the overwhelming fire, the squad can maneuver, close the distance, and kill the enemy. This volume of fire is not inherently accurate. It uses a beaten zone that’s measured in feet. If a SAW gunner is off-target or cannot control the weapon, their fire may not be effective.

The suppression theory behind the M27 IAR is suppression through accuracy. The rifle firing short, controlled bursts or even single shots in an accurate manner will pin down an enemy just as effectively as a belt-fed machine gun. As an automatic rifle, the gun can still operate at full-auto fire to provide overwhelming fire at the beginning of the firefight.

The M27 IAR has its own downsides. The first is the fact it’s a rifle that feeds from a 30 round magazine. This results in more reloads required, which can create a gap of fire and a lag in suppression. Additionally, the M249 uses a quick change barrel to preserve the barrel life when firing in a sustained manner.

An important note is that the Marine Corps infantry now issues the M27 en masse to squads. Now every member of the squad has an automatic rifle to provide suppressing fire.


Without a doubt, the M27 IAR is the more accurate weapon. The closed bolt and free-floating barrel give the M27 IAR an inherent advantage in the accuracy department. The M249 SAWs open bolt, full auto-only design, does not create the most accurate of weapons. Admittedly it’s not supposed to be an intensely accurate weapon.

The Marine Corps immediately realized that the M27 IAR was extremely accurate. It’s more accurate than the standard service rifle. This led the Marine Corps to create the M38 DMR. The difference between the M27 and M38 is the optic. The M38 uses a Leupold 2.5-10X optic.

Weight and Ergonomics

One of the biggest appeals of the M27 IAR was the drastic reduction in weight and bulk. An M27 IAR weighs about 9 pounds loaded, and the M249 weighs a brutal 22 pounds fully loaded. Admittedly 22 pounds is fairly light for a machine gun but heavy compared to a 9-pound rifle.

The M27 IAR better suits the need for modern warfare. The lighter rifle allows the weapon to be better in close-quarter’s environments like in urban warfare and in and out of buildings. Clearing rooms and fighting in the streets is much easier with a lighter rifle.

The SAW’s weight often forced you to take a supported position in the kneeling or in the prone and use bipods for remotely accurate fire. The M27 IAR makes it easy to fire from the standing in unsupported positions. Full auto fire may still be limited, but the semi-auto settings ensure it’s plenty controllable.

FN designed the M249 to be a very ergonomic and easy-to-use platform. From experience, I can tell you that the M249 is easy to use with a side-mounted charging handle, a simple cross-bolt safety, and that’s about it. What is awkward is reloading and carrying the beast. Reloads with belt feds are slow but less frequent due to the higher capacity belt-fed design.

The M27 IAR uses AR-style ergonomics that make it naturally very easy to use. Carrying the weapon is also much simpler, and reloading magazines might occur more but is much faster. Plus, unlike the SAW, the M27 can be easily reloaded in any position and even on the move.


Oh boy, the M249 SAW can be a very reliable weapon. The downside is that many SAWs in the armory are older than the Marines carrying them. When a SAW is newer, it tends to function well. When beat to hell, the weapon predictably fails quite often.

A new SAW versus the M27 would still likely see the M27 having a slight advantage. The M27 utilizes a closed bolt design, which tends to be more reliable than open bolt designs.

In Action

Marines in Afghanistan were initially unsure about the M27, but their confidence grew as they carried the weapon more. The Marines at one point declared they would request mast, a formal way to jump the chain of command with an issue if the Marine Corps took the M27s away.

The Marine Corps has switched to training the Marines to engage with precision suppression fire guided by optics rather than engaging with overwhelming fire superiority. The M27 IAR has become a hit with Marines and is now the combat arms service rifle. I think it’s clear the M27 IAR outperforms the M249 in many ways. The Marines will keep several SAWs in the armory just in case they need that belt-fed fire superiority.

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