FN M249: Putting Brass In The Grass For Freedom For Half A Century

In military conflicts, the concept of fire superiority is to deliver a greater volume of fire upon your enemy than they’re inflicting upon you. It’s a critical element of military strategy. Once you’ve established fire superiority, then by definition your enemy will bleed resources. Thus, fire superiority begets even more fire superiority, until your enemy has been defeated and you achieve your objective.

For ground forces, machine guns are a key component of gaining fire superiority, providing the ability to deliver high rates of fire for extended periods of time. This is achieved by firearms designed specifically for this purpose, feeding from belts of ammunition that can seem to be endless if you’re on the business end of one.

In the 1960s, American forces employed the M2 heavy machine gun in .50BMG and the M60 general-purpose machine gun in 7.62mm; both were bulky, heavy, and crew-served weapon systems. 

The Army wanted a light machine gun that could be carried and employed by a single individual, as part of infantry squads — the Squad Automatic Weapon. This took some time to become a reality; after first considering a new 6mm cartridge, the Army settled on 5.56 NATO and conducted tests and trials throughout the 1970s. 

Across the pond, Ernest Vervier of FN Herstal designed a light machine gun they coined the FN Minimi — long before Dr. Evil co-opted the name; it’s actually an abbreviation of “mini machine gun” in French. Submitted to the Army’s trials, the Minimi eventually beat out the HK 21, M16 HBAR, and Rodman Laboratories XM235 to become the M249 Squad Automatic Weapon. The Army began fielding the M249 SAW in 1984, followed by the Marine Corps in 1985. FN manufactured them in South Carolina.

The M249 has made its presence known in American hands on the battlefield ever since the first Gulf War, and in particular throughout the Forever Wars. However, while the FN Minimi continues in service around the globe, the sun is setting for the M249. In 2009, the Marine Corps selected Heckler & Koch to build the M27 Infantry Automatic Rifle, based on the HK416. 

While it’s magazine-fed, it’s partially replacing the M249s in service, not to mention M4s as well. Meanwhile, the Army initiated the Next Generation Squad Weapon Program in 2019 to replace the M249, awarding SIG Sauer a contract for the new XM250 machine gun, chambered in 6.8x51mm. It’s currently undergoing operational testing by troops in the 101st Airborne Division and 75th Ranger Regiment.

M249 FTW

The M249 is a belt-fed light machine gun chambered in 5.56 NATO, firing from an open bolt. With closed-bolt systems that you’re accustomed to in normal semi-automatic guns, a round is first loaded in the chamber to make it ready, then ignited by a hammer or striker when the trigger is pressed. 

On the other hand, when ready to fire, an open-bolt system has an empty chamber with the bolt retracted. When you press the trigger, it releases the bolt assembly, which strips a round from the belt or magazine, then chambers and discharges it — a machine gun will repeat this process until you release the trigger or run out of ammunition. 

Air-cooled and gas-operated, the M249 incorporates an AK-style long-stroke gas piston, flipping it upside down to accommodate feeding from a belt. The rotating bolt provides lock-up and a bit of a delay before extraction. The original version had an adjustable gas system — later removed — with normal and adverse settings that resulted in cyclic rates of 700 to 850 or 950 to 1,150 rounds per minute, respectively.  

The appearance of U.S. Department of Defense (DoD) visual information does not imply or constitute DoD endorsement.

The M249 has a stamped sheet metal receiver, with a Picatinny top rail eventually added to the feed tray cover. Iron sights include a hooded front sight and a rear aperture, with an elevation drum to adjust between 300 and 1,000 meters. 

Above the pistol grip is a cross-bolt safety to switch between safe and fire; there’s no semi-auto mode. A built-in, multi-position, spring-loaded bipod folds into the handguard. A carry handle is attached to the rear of the barrel assembly and can be folded in later versions of the M249. The fixed plastic buttstock is modeled after the M240 and features a folding shoulder rest.

The charging handle is on the right side, while ammo feeds from the left. Belted ammunition utilizes M27 disintegrating metal links, smaller versions of the trusty 7.62 NATO M13 links. The links have interlocking loops held in place by the rounds that are pushed into place. As each round is fed into the weapon, its link falls away.

To load the M249, flip open the feed tray cover by squeezing the latches at the rear to release it. Retract the charging handle, flip up the feed tray, and inspect the chamber. Grab the linked belt of ammo and ensure the exposed brass is facing downward — “brass to the grass,” as taught in the military. 

Place the belt on the feed tray with the first round snugged against the cartridge stop; retaining pawls will hold it in place. Securely close the feed tray cover, and you’re ready to rock.

When you press the trigger and release the sear, the bolt assembly lurches forward, thanks to the recoil spring. As it moves forward, the bolt strips a round off the belt, chambering it and rotating to lock the lugs. 

A roller on top of the bolt rides in a track on the feed lever underneath the feed tray cover, causing the feed lever and pawls to advance the belt by one position. The chambered round is discharged by the firing pin, and gases bleed off the gas port in the barrel, through the gas regulator, and drive the long-stroke piston backward. 

This causes the bolt to retract, the ejector to kick the spent brass out, a link to fall away, and the cycle to repeat. When empty, the bolt will not lock back.

The standard plastic ammo boxes hold 200 rounds of belted ammo and clip into place underneath the receiver in front of the trigger guard; depress a locking latch on the box to remove it. As an alternative to the fiddly hard plastic ones, you can get 100- and 200-round soft pouches, affectionately referred to by soldiers as “nutsacks.” 

Interestingly, there’s also a magazine well on the left side underneath the feed tray, so if you’re in a pinch and out of belted ammo, you can use a standard STANAG magazine — though M249s aren’t known for stellar reliability when feeding from magazines; they really chew them up. The dust cover for the magwell also functions as the magazine catch.

A necessity for machine guns like the M249, the barrel is easily swapped out. Simply retract the bolt, pull back on the barrel latch lever, then grab the carry handle and pull out the barrel. The standard barrel is 18 inches long, not including the muzzle device and as measured for NFA purposes.

While the M60 was 44 inches long and 23 pounds, the M249 is just under 41 inches and 17 pounds. Plus, 5.56 ammo is roughly half the weight of 7.62.

FIELDSTRIPPING THE SAW

Fieldstripping the M249 for cleaning and maintenance is straightforward and requires no tools. In fact, if you search YouTube, you’ll find examples of service members racing to disassemble and reassemble the M249 in less than a minute.

First, ensure the weapon is clear. Make sure the safety selector is on safe and the bolt is cocked to the rear. Open the feed tray cover and remove any source of ammunition. Open the feed tray as well and examine the receiver and chamber for brass, links, or ammo. While holding the charging handle, place the weapon on fire and press the trigger to release the bolt carrier assembly to the forward position.

Push the upper take down pin toward the left side of the gun. It’s captive, so it won’t come out completely. Now, you can rotate the buttstock down, or you can push the lower take down pin to the left as well to remove the buttstock entirely. If you do that, you can then pull the trigger assembly out as well. 

With the buttstock out of the way, the innards of the M249 will now be exposed on the aft end of the receiver. Press in and up on the guide rod and spring assembly in the lower part of the receiver to release it, then pull it out. Slide the spring off of the guide rod.

Next, pull back on the charging handle and remove the bolt carrier/piston assembly. Press in on the bolt and rotate it to pull it out of the carrier. Use a punch to drift out the firing pin retaining pin to remove the firing pin and spring.

Remove the barrel as described earlier. You can detach the heat shield by rotating it up and off the barrel. To remove the gas cylinder, grab the knurled end, then rotate and pull on it. Once you’ve pulled it entirely out of the receiver, you can also deploy the bipod then slide it forward.

Perform all these steps in reverse to reassemble the M249.

M249 VARIANTS

After early complaints about the M249 as originally delivered, the Army quickly rolled out a Product Improvement Program. This included swapping in the plastic fixed buttstock with a new hydraulic buffer and removing the adjustable gas system, along with numerous other tweaks. 

These and other refinements continued to be rolled out over time to improve ergonomics and durability. Picatinny rails were added to the feed cover and handguard to allow optics and accessories to be mounted to the weapon.  

The M249 Para was introduced for units requiring a more compact package at 35 inches overall. The fixed buttstock was replaced with a telescoping metal stock, and the barrel was shortened from 18 to 13.7 inches. 

Due to the design of the M249, these parts are easily swapped in the field — for the buttstock, simply yank out both take down pins in the rear and swap them out. For the barrel, just remove the old one and install the new shorty, just like a normal barrel change.

A lightweight version was fielded for SOCOM, called the M249 SPW. It called for the removal of the carry handle, magazine well, and vehicular mounting lugs. The barrel profile was lightened and the bipod made detachable. 

This saved about 3 pounds compared to the M249 Para.

Further refinements to the M249 SPW resulted in the Mk 46, adopted by SOCOM. The plastic fixed buttstock was restored and the forend revised. 

The Mod 0 version deleted the carrying handle and added a quad-rail forend. It was followed by the Mod 1, which restored the carry handle and original heat shield, switching to rails at 3, 6, and 9 o’clock on the forend.

BELT-FED LIFE GOALS

In 2016, FN America released a number of civilian-legal firearms in its Military Collector series — including semi-auto versions of the M16, M4, and M249. The latter, called the M249S, is what we see here. 

The FN M249S had to be modified from the original to constrain it to semi-automatic mode — legally it’s just a regular, albeit large and heavy, semi-automatic rifle that happens to be belt-fed. FN achieved this by revising it to operate as a closed-bolt system. 

The bolt assembly is no longer held back by the sear and always returns forward to chamber a round. FN added a slide hammer assembly behind the bolt; pressing the trigger releases it forward to strike the firing pin and discharge the round in the chamber. They also added a second spring on the guide rod for the slide hammer. Additionally, FN made other changes to prevent the installation of full-auto goodies from the original.

As the M249S is a closed-bolt system, it changes the manual of arms that SAW gunners may be used to. After loading a belt or magazine, to make ready you’ll need to charge the weapon to chamber a round. 

When unloading and making the M249S safe, you must be sure to rack the round out of the chamber after removing the ammunition source. Also, you can’t lock the bolt to the rear, so FN provides a plastic block to insert in the magwell to hold it back — for instance, if you wish to remove the barrel without the benefit of a third hand.

The M249 is hardly a precision weapon system; the trigger pull on our example was a hefty 11 pounds. But loaded up, the whole thing is awfully heavy, so it’s not bothersome. The M249S is an absolute blast to shoot, even if it doesn’t have freedom mode. We challenge anyone to get behind this thing, start slinging lead downrange with brass and links scattering about, and not start smiling immediately. In fact, involuntary chuckling is pretty likely as well.

Of course, this being RECOIL Magazine, we couldn’t leave our M249S bone stock, even if the gun itself is as rare as chicken teeth. First, it needed an optic. So, we affixed the product we selected for our Best of SHOT Show 2023 award — the Holosun DRS-TH. A hybrid fusion optic, it combines an enclosed-emitter red dot with a thermal sensor that can overlay its image over what you see through the glass. 

You can run it like a normal red dot, with the usual features you’re accustomed to from Holosun. Or you can activate the secondary optical system to overlay the thermal image, with settings for white hot, black hot, fusion, highlight, and outline. While the DRS is awfully chunky on a regular rifle, it looks at home on a 249. It’s an impressive piece of technology that lets you get your Predator on.

As civilized folk, we also needed a suppressor for it. So, we spun off the flash hider and replaced it with a taper mount flash hider that mates with Radical Defense’s new GPS Suppressor, from its line of products specifically designed for belt-fed machine guns. 

It’s 3D printed with Haynes 282 superalloy and available with an I/R non-reflective coating. Full-auto rated, it handles calibers up to .338NM. It features forward venting for pressure stabilization and reduced back pressure. 

It also has an integrated flash hider to reduce flash signature and ground disturbance. It’s 7.5 inches long, 1.75 inches in diameter, and 1.5 pounds.

Finally, since brass and links are precious metals for civilians, we attached the new JJ249 brass catcher from Kinetic Energy Tools to easily collect them during range trips. It’s made of 1000D Cordura and has a metal frame that attaches to the tripod mounts on the M249 using quick detach pins. 

There’s a zippered dump panel on the bottom, so  you can empty casings and links without detaching the catcher from the gun — place the larger carrying case underneath as a convenient dump bag.

At a retail price just over 10 grand, the FN M249S isn’t a question of need. You don’t need one. But you damn well want one. Props to FN America for making it commercially available. It’s unquestionably badass and a worthy addition to your life goals. 

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