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M240B Machine Gun: Machine Gunner Review

Our resident machine gunner runs down the pros and cons of the military's M240B. Ever wanted to know what it's like to run a machine gun? Come find out.

What’s my favorite gun of all time? I mean ALL TIME!

Not my favorite from my collection and not my favorite I can purchase at any gun store. I mean, my real favorite gun.

Effective Range Shotgun
I do love shotguns, but my fave gun is not a shotgun.

It’s the M240B.

For five years, I served as a United States Marine Machine gunner, and I loved my job.

I got my hands on guns like the M16A4, the M4, a Mossberg 590A1, an M9, and of course the M249 SAW, the M240B, the M2, and MK19.

Shooting a belt-fed machine gun is something everyone should experience at least once. It’s so much fun.

I deployed with the M240B twice and carried it as a gunner in a machine gun team. Not to mention, I also used it to instruct non-machine gunners and foreign military forces.

It’s gone with me on top of mountains in Africa, stormed beaches, and crossed the Helmand River.

We became close friends. While you can’t go down to your friendly gun store and grab one of these things, they are neat pieces of machinery.

So, I figured, why not break this gun down and talk about its cool features and look at its role as the main weapon of a machine gunner in a line company.

Ready to learn more? Well, keep reading.

Table of Contents


Breaking Down the M240B

FN Herstal built the original FN MAG machine gun.


When the United States military wanted to replace the M60, they settled on the M240. Without a doubt, the M240 is superior in nearly every way.

The M240 operates on a long-stroke gas piston system, operating on an open bolt system.

Officially, the M240 serves as a gas-operated, belt-fed, open bolt, air-cooled, crew-served, fixed headspace general-purpose machine gun.

General Purpose Machine Gun, or GPMG, is a concept to have one machine gun to serve many roles.

Travis M240B Machine Gun Military

As such, the M240 is found in the hands of foot-based infantry, on trucks, on guard posts, on helicopters, on tanks, APCs, AAVs, boats, and more.

The M240B model was built upon the Gulf model and implemented a hydraulic buffer system to help reduce recoil. It also offered a Picatinny rail system and a simplified gas system.

M240 Navy
M240 Navy

M240B rails are often adorned with laser aiming devices like PEQ15s.

The gun comes with an integral bipod — easily connected to the classic M122 tripod. In training, Marines use the tripod extensively, but in combat, it never left our FOB.

Belts of ammunition feed from the left, and gunners load the belt with the cover closed or opened.

Loading with the cover closed allows the machine gun team to quietly load the gun and protects any optics from a hot barrel.

M240B Barrel & Belts

Speaking of barrels, the M240B’s quick-change barrel ensures gunners don’t burn the barrel down.

All a runner needs to do is hit the barrel release, pop the handle up with a karate chop, and remove the barrel – replacing it with a new, cooler barrel takes even less time and is done with ease.

Capacity varies depending on just how many belts you want to link together.

Travis M240B Machine Gun Military
(Photo: DoD)

When I patrolled, I carried a 50-round belt loaded into a cloth sack that we crudely called a nutsack.

Fifty rounds acted as a “starter belt” so the gunner could lay down suppressing fire immediately.

Belts can be connected to ensure the gun never actually runs out of ammunition, and a good team can keep an M24B running for nearly forever.

The M240B qualifies as a crew-served weapon, and by doctrine, the gun has three crew members.

One serves as gunner, one as ammo man, and another as team leader who is also an A-Gunner.

Travis M240B Machine Gun Military
(Photo: DoD)

Team leaders help load the gun, change the barrel, control the rate of fire, and pass orders from the squad leader.

The ammo man provides rear security and brings ammo as necessary while the gunner fires the weapon (obviously).

While that’s the most fun job in the team, it also necessitates the gunner carrying the gun regularly.

At the Range and In Combat

At the range, the M240B offers only full-automatic fire.

A simple cross-bolt safety takes the gun from safe to full-auto, with a cyclic rate of 550 to 650 rounds per minute.

It’s quite controllable, and an experienced gunner can fire controlled bursts to land accurate fire on target.

Travis M240B Machine Gun Military

Controlling the weapon on both bipods and tripods does take some training and experience, though.

Marines advise right, tight, and down when using a tripod.

With a bipod, you grab the stock with your non-dominant hand and shove it into your shoulder as you fire.

Anything fully automatic takes some practice to control. Without proper control, the M240B will beat you up and toss you around.

You’ll open up your beaten zone so much; the gun becomes much less effective.


When Marines exercise proper recoil mitigation and control, the M240B proves extremely accurate.

With a tripod and a good firing position, the M240B can hit targets out to 1,800-meters. My squad and I have done just that with an old burned-up car being our target.

The sound of a burst striking metal carries quite far and makes it easy to know when you’ve made contact.

Travis M240B Machine Gun Military
(Photo: DoD)

Cars are big targets, but to be fair, it was over a mile away, and I was using iron sights.

My team leader used binoculars to walk me onto the target. Once we were on target, we laid down hate and discontent.

Lots of our ranges offered a multitude of reactive targets that fell when hit.

We had zero issues hitting these man-sized targets at 300- to 500-yards with just a few bursts.

Not to brag, but on one range, my team was so efficient with hitting targets our maneuvering rifleman had nothing to shoot.

Travis M240B Machine Gun Military

The peep sights are surprisingly fine and function well to get the gunner on target.

Admittedly once on target, you can break your sight picture. Within 600-yards, the tracers from the 7.62 belts can get you on target without the need for sights.

An optics rail over the top allows for the use of day and night optics.

The Marine Corps adopted a Trijicon Machine Gun Day optic, but I hated it.

Trijicon Machine Gun Day optic (Photo: Trijicon)

It felt like 3-pounds of waste on a gun that doesn’t need an optic to do its job, but maybe I’m just a Luddite.

Control and practice make the M240B an extremely accurate weapon, even as the weapon heats up.

When things get too hot, we swap barrels and give the first one time to cool. In fact, I would say this takes more skill to shoot accurately than any other weapon I’ve handled.

The M240B, Bipod Required. Image Source: Military.com
The M240B, Bipod Required. (Photo: Military.com)


Ergonomics are all over the place. But as a machine gun, it’s not exactly made to be ergonomic.

What it excels at is reliably laying down fire.

Loading from the left makes it easy for the A-Gunner to keep the weapon loaded and firing.

Pop the top, and the A-Gunner can drop a new belt in place.

A solo gunner can reload the weapon, but it’s a slower process because of the 50-inch length of the weapon. The shooter must move around the weapon to do so.

Travis M240B Machine Gun Military

The right side charging handle requires the shooter’s hand to leave the firing position.

You can’t do the Haley under the gun charge with this thing.

Links and casings eject out the bottom of the gun and create a nice little pile beneath the gun, preventing the casing from being flung into the gunner and A-Gunner.

The bipods lock in place under the handguard easily enough and look massive.

Their large size allows them to lock into place and pop in and out.

It’s rapid to drop and get into a hasty bipod prone and start laying down fire as necessary.

Magpul MLOK Bipod
Good ole bipods.

Let’s be real…everything on the M240 looks and feels massive.

The charging handle, safety, stock, and top cover are huge and easy to activate and use.

That big stock provides solid lockup into your shoulder and makes balancing out the recoil easier.

I’m always suspicious when I see rifle stocks on machine guns. Like, how comfortable is a stock designed for a 5.56 rifle going to work on a 7.62 machine gun?

Ergonomics are strong….except for the 27.1-pound total weight of the gun.

Travis M240B Machine Gun Military

A spare barrel weighs another 6.6-pounds. In short, it’s a hefty gun. After carrying for miles every day on foot, I had killer legs.

It’s also a gun full of corners, sharp edges, ridges, bolts, and all sorts of stuff that pokes and prods as you carry it.

There is no way to carry it for long periods completely comfortably.


Every machine gunner finds his way of doing it, though. I relied a lot on a two-point sling, carting it around more like a rifle.

As a 49.7-inch weapon, maneuvering in vehicles, buildings, and even alleys was never fun.

This gun will never be used to clear rooms. Well, until we train gorillas to use them, of course.


My M240B never failed me. In literally tens of thousands of government-sponsored rounds, the gun always went bang.

I’ve fired so much ammo through one in such a short time; I lit my cigarette off the barrel…while it was raining.

Travis M240B Machine Gun Military

It needs just a little lube every now and then, but it will keep going.

The M240B’s long-stroke gas piston system doesn’t need much love to keep running either.

At a training event in UAE, a sand storm set in on us. This sandstorm disabled nearly every other weapon, but the M240Bs still fired without remorse.

That’s not terrifying at all….

I’ve used one in the humid hills of Spain, sand-ridden mountains of Djibouti, and frigid temperatures of Romania without complaint.

They work full of dirt, mud, and sand without argument.

By the Numbers

Ergonomics: 4/5

It’s so dang heavy! Other than that, the weapon’s layout makes it easy to use, load, and fire. It’s not fun to carry, but boy, oh boy, it’s fun to shoot. The big controls work well with gloves and make it easy to keep the gun running.

Reliability: 5/5

A little CLP helps ensure the gun runs, but I’ve never seen it fail — even when forced to feed blanks in austere environments and tasked with eating hundreds of rounds in a short period.

Accuracy: 4/5

It’s only a step down from a sniper rifle when mounted to a tripod. By itself, the gun can be tough to control enough to shoot accurately without plenty of experience. However, with a max effective range of 1,800 meters, it’s tough to beat.

Looks: 2/5

It’s a pig, an ugly pig. It doesn’t have much going in the looks department, but you can see its World War II heritage.

Overall: 5/5

Do I have a bias for the M240B? Yep. A big one.


I love this gun without shame and find it the most reliable machine gun in the USMC’s arsenal. It works better than the SAW, the M2, and the MK19, providing platoon-level firepower in a man-portable package.

Travis M240B Machine Gun Military

I love the M240B, and I loved being a machine gunner. There is a deep satisfaction you get when you’re carrying the biggest gun in the gunfight.

It’s an outstanding piece of machinery, and I don’t see it going anywhere anytime soon.

Any other gunners in the group? Let us know what you think about the M240B in the comments below. Or check out my machine gunner’s analysis of the new FN Herstal Evolys.

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5 Leave a Reply

  • Commenter Avatar
    Lefty 60 Gunner

    I loved humping The Pig!

    March 8, 2023 10:14 pm
  • Commenter Avatar
    Big Frank

    I was a small arms repairman in the army when all branches of the service still used the M60 as their GPMG (or Medium MG). But we had M240s as coax MGs in all the M60A1, M60A3, and M1 tanks. Not M240A, B, C, D, or E, just plain M240. They're a heck of a good gun, and the biggest problem I saw was operator malfunctions. Like when some tanker who wasn't authorized to take things apart, took the buffer assembly apart and stacked all the Belleville washers in it like this (((((((((((( instead of this )()()()()()( when they put it back together. The washers stacked up like dishes, making the stack a lot shorter, and when the bolt and op-rod slammed into the buffer cap, there was no spring to absorb the impact. I did some work with a Swiss pattern file to smooth out the damage in and around the hole where the op-rod tried to go inside the buffer, and after proper assembly had it fixed up good as new.

    The only drwback about the M240B I know of is that it weighs 4.5 pounds more than the M60 machine gun. And I don't mean a lightweight M60, but the original Pig, like they adopted in 1957 and used in Vietnam. On the plus side, no one ever walked into the shop with an M240 telling me they had a runaway gun like they did with an M60 one time. One of the guys I worked with said, "You better go catch it!" Some grunt who wasn't authorized to take stuff apart (Is anyone sensing a trend here?) took the sear out of the pistol grip, flipped it around backward and put it back in upside down. I had no idea that was even possible until I saw it. So when they pulled the charging handle back and let go, it fired until it ran out of ammo, or until someone snapped off the belt. No one ever touched the trigger as far as I know. They didn't have to since it wasn't connected to anything. I like that you can close the cover on the M240 before you cock it. On the M60, you have to cock it first or the op-rod roller won't be in the feed arm track, and if you yank on the charging handle it will bend things up. These geniuses were holding the bolt back by hand since the sear wasn't holding it, put the belt in, closed the cover, and then let fly. It took 2 people to screw that up, the gunner and loader together.

    September 21, 2022 6:40 pm
  • Commenter Avatar

    Rah, from your 2111.

    September 26, 2021 6:47 am
  • Commenter Avatar

    thank you ..but how do I get one??

    August 19, 2021 8:15 pm
  • Commenter Avatar
    Jack Toffmore

    Great write-up. Thank you for your service as well!

    August 16, 2021 7:25 pm
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