marine infantryman training on 50 caliber machine guns

Marine Machine Gunner (MOS 0331): Job Description And Summary

Understanding how the Marine Corps infantry operates can be a bit tricky if you are not familiar with the different functions of the personnel involved. What most people find it difficult to understand is the difference between a marine machine gunner and a rifleman.

Most people assume that marine machine gunners perform the same functions as a rifleman, when it fact there are some notable differences.

The most critical work of Marine Corps infantry marine machine gunner, aka MOS 0331 or ’31 by their infantry platoon mates, is handling large machine guns in any combat.

They help riflemen move around the battlefield freely and without being overwhelmed by enemy forces.

Let’s learn a bit more about what exactly 0331’s do, how to become one, the actual machine guns they carry, and what life is like as a machine gunner.

MOS 0331 Requirements

Strength And Size

The most critical requirement of an 0331 is they need to be strong.

0331 training
Marine Corps 0331 firing a M249 light machine gun. Image:

Machine gunners are the guys doing the heavy lifting, and therefore need to be bigger and stronger than the average rifleman.

It’s not uncommon for the largest guys in the platoon to be assigned as machine gunners right out of the gate.

That is to say, if you’re 6’4″ and 230 lbs., you’ll likely end up as a 0331.

Related Article: 13 Pros And Cons Of Joining The Marine Corps

Age, ASVAB, And Height / Weight

For starters, anyone between the age of 17 and 46 can become a marine machine gunner.

To become a machine marine machine gunner, one needs to have a relatively high score of 80 and above on the General technical section of the Armed Services Vocational Aptitude Battery, or ASVAB.

For men, the height ranges between 56 and 82 inches while the weight varies between 85lbs and 263 lbs. For women, on the other hand, the height ranges between 56 and 82 inches while the weight ranges between 85 and 248lbs.

If a marine machine gunner candidate fails the height or weight, then the two can be waived if the machine gunner passes all the other tests. With regards to body fats standards, a male marine machine gunner candidate should not exceed 18 percent of the body while the female should not exceed 26 percent of the body.

The fat composition can, however, be disregarded if the candidate masters all the physical fitness test and the combat fitness tests and the score has to be above 285 or higher in both tests.

Where Is 0331 Training?

A machine gunner has to attend the machine Gunner course offered at the school of infantry and a camp in Lejeune, North California or Camp Pendleton in California.

0331 carrying a saw
0331 carrying a Squad Automatic Weapon, or SAW. Image:

The training base of a machine gunner depends on a person’s home base.

Related ArticleHollywood Marines: San Diego Vs. Parris Island Marines

At the camp, machine gunners are trained in fire control, military tactics and fire control systems and most importantly, how to become a significant team player within the use corps fire teams which consist of either fire team weapons or rifle platoon.

Also as part of the fitness test, a marine machine gunner needs to take part and pass the physical fitness test and combat fitness test.

A physical fitness test consists of crunches that include, and a mile timed run. ACFT, on the other hand, consists of 880-yard run, 30-pound ammo can lifts, and a 300 yard under fire maneuver.

How’s Life As A 0331?

The life of a machine gunner is not as easy as one may assume, and this can be inferred from the fact that they need to carry around a weapon and ammunition that weighs significantly more than what riflemen carry.

An average machine gunners weapon weighs 24 lbs, and includes a large amount of ammunition.

A 0331’s work is to support riflemen when they’re under attack from a large contingent of forces.

They can sit on a hill with a vantage point of view and lay down a suppressing amount of fire that can keep an advancing enemy force at bay.

As a result, they are often carrying as many as 600 5.56 mm rounds at a time.

Also, 0331’s goes through a complicated training process and therefore need a lot of physical and mental conditioning, and they can, therefore, make extremely god riflemen.

Related Article: 10 Best Marine Corps Jobs For Civilian Life

Machine gunners are always put into different categories based on age group and sex. Moreover, marine machine gunners are ranked and paid differently. The lowest rank of a machine gunner is private who earns a minimum salary of 1536 US Dollars while the highest ran is a sergeant who earns a minimum wage of 5176.

Marine gunners can patrol whether mounted or dismounted and always operate in three-person teams where the team leader leads the team and directs the machine gunners fire. The second person, on the other hand, employs the M240 gun while the third person carries spare ammunition and barrel for the gunner as well as assisting in deploying and employing a machine gun.

The machine gunner is always a critical force multiplier in the platoon or squad. Life in combats can become tricky, and survival is the most important thing. During combats, machine gunners should be prepared to fight in close quarters when on foot, on mounted positions or even from aircraft.

Typical Machine Guns Carried By 0331’s

Some of the weapons used by machine gunners include:

  • M2 Browning
  • M240
  • MK 19 Grenade Launcher
  • M249E4

7.62 mm medium machine gun, the 50 caliber, and 40mm heavy machine guns. The M2. 50-caliber is a heavy, automatic, air cooled and recoil operated gun with adjustable headspace. It is crew transportable with a limited number or amount of ammunition on short distances. Ammunition is fed using a disintegrating metallic link belt, and the gun has a backplate with bolt latch release, spade grips, and trigger and may be mounted on most vehicles and grounds.

The 7.62 machine gun serves the role of a medium machine and is usually fired on a tripod mounting and is air-cooled, fully automatic belt gas operated weapon. The machine gun can also sustain the high burst of fire, and it consists of two barrels which can be easily changed to avoid overheating which can cause cook-off and consequently a reduction in barrel life.

Another machine used by machine gunners is the MK19 Grenade Machine Gun. This is a fully automatic, integrated metallic link-belt fed, air coiled blowback gun that can fire a variety 40mm grenades. The gun can be transported over short distances and with a limited amount of ammunition. The machine guns grenade can pierce any armor up to two inches thick and can also produce fragments to kill personnel within five meters and wound personnel from 15 meters of any point of impact.


A marine machine gunner (0331) plays an essential role in combats and before becoming a gunner, one has to undergo specific training offers in camps. The work of a machine gunner is to carry a rifle for riflemen and can take part in combats. During camp training, the gunners should pass different tests before finally going into the battlefield. The remuneration process of gunners depends on their ranks. Since gunners undergo intense training and interact with machines during combats and they can, therefore, make good riflemen.

Marine Machine Gunner (MOS 0331): Job Description And Summary
5 (100%) 3 vote[s]

Jeff E.
Jeff E.
Jeff served with the Marine Corps Reserves as an Infantryman with Kilo Co. 3rd Battalion 23rd Marines from 1997 to 2003. 3/23 was deployed to Iraq in 2003 and served primarily in the Wasit Province of Iraq. Since exiting, Jeff has served as a non-profit manager in the area of foster care and adoption.

Leave a Reply

Your email address will not be published. Required fields are marked *