The Virtual Navy
Commander Naval Education and Training
Assistant Gunner Course
In this course you will learn the technique of resuplying your team with amunition. You will learn how to use the M-249 and M-240 as you will use these if the Heavy Weapons Specialist is injured or killed in combat. You have already at this point qualified with the M-16 and will carry this until the HWS is injured or killed.
M-249
M249 SAW:
The M249 is an air-cooled, gas-operated, fully-automatic-only firearm that fires from an open bolt position. It can accept belts of linked 5.56x45mm NATO (.223) ammunition through the top-mounted feed tray or M16-type magazines through the side-mounted port. The latter allows a SAW gunner to use riflemens' magazines in an emergency if he runs out of belted ammunition, though this often causes jams as the magazine spring cannot adequately keep up with the weapon's high rate of fire. Linked ammunition can be fed from either a loose belt or from a plastic box (6.92lb) (or cloth pouch) for 200 rounds, clipped under the receiver. The hard plastic box has issues with being insecurely attached and by producing noise with movement in its standard form. The M249 SAW features a built-in bipod and a tripod-mounting lug for supported fire, as well as a quick change barrel that helps prevent overheating during sustained fire. Barrels are engaged and disengaged by rotating the built-in handle, and a spare is normally carried slung in an "A-bag" by the gunner or his assistant. The forearm is designed to contain a small cleaning kit for field use, though it may not be stored there in practice.
The gun has good firepower for its size. The latest reports on failures of M249 SAW weapons in Iraq are sometimes attributed to the age of the weapons used, and sometimes to the dusty environment in Iraq and Afghanistan. Most of the current-issue M249s in U.S. Army are more than 10 years old, which is not excessively old for a service firearm, but can reduce reliability. There have been issues with its performance at other times, particularly earlier in its development.
For training exercises, the M249 is used with the M249 Blank Firing Adaptor (BFA), essentially a steel plug which screws into the muzzle and partially blocks it. (While standard blank firing adaptors for the M16 and M4 family of weapons will fit into the barrel of the M249 SAW, their use has been abandoned in favor of a SAW-specific BFA, due to the risk of catastrophic failure of the weaker rifle BFA, which is not durable enough for sustained automatic fire.) Gas-operated weapons rely on the projectile to trap gas pressure in the system as it leaves the barrel; without this, there will be insufficient pressure to cycle the weapon. U.S. M249s are sometimes fitted with the M145 MGO, a low-power optic that fits on via a top M1913 rail, when the rail is fitted. The regular M249 does not have a rail, however. The M249 mod kit increases the weight to 16.41 pounds.
United States military doctrine describes 3,600 m as the maximum range. Effective ranges include 800 m for a point target, 1000 m for an area target, and 600 m for suppression (suppression fire is attained by keeping the maximum height of the rounds no more than 1 m off the ground). Tracer ammunition burnout is at 900 m, however. The advised rates of fire are 85 rounds per minute with no barrel changes. With a barrel change every two minutes, this increases to 200 rounds per minute. For a barrel change every minute, the rate of fire can go up to 850 rounds per minute, which is approximately equal to the cyclic rate of fire, at about 850 to 900 round/min.
In addition to its traditional use as an infantry weapon, the M249 is also sometimes used as a vehicle-mounted weapon, most often on Humvees, either in the normal roof mounting (manually or remotely operated as part of a system such as the CROWS mount, sometimes in addition to heavier weapons such as an M2 Browning machine gun), or on a swing arm mounting accessible by the front passenger seat. It is also one of the weapons that can be mounted on the SWORDS robot.
M-240
Manufactured by Fabrique Nationale, the FN MAG was chosen by the U.S. military for different roles after large world-wide searches and competitions. It has mainly replaced the M60 in most roles, though it replaced some other machine guns in the co-axial position. M60s have remained in use, but they are being slowly phased out and replaced by the newer M240s as they wear out.
The M240 is a belt-fed, gas-operated, air-cooled, crew-served, established headspace weapon. It is compatible only with the M13 Link system, also used by many other western (especially NATO) machine gun designs. Its functionality is demonstrated by its ability to be mounted on the M122A1 tripod, a bipod, on vehicles, or on aircraft. The M60 is still used as a door gun on Army helicopters, however.
It was first adopted in 1977 by the U.S. Army as a co-axial tank gun, and slowly adopted for more applications in 1980s and 1990s. The M240 and M240E1 were adopted for use on vehicles. This led to further adoption in more uses, especially for the Army and Marine infantry. While possessing many of the same basic characteristics as its predecessor, the durability of the M240 system results in superior reliability when compared to the M60. The M240 actually has a more complex gas system than M60s, but can function better with lower maintenance with higher reliability, though this comes at greater cost and weight.
Compared to other machine guns, its rating of 26,000 Mean Rounds Between Failure (MRBF) is quite high for its weight—in the 1970s when it was first adopted it achieved about 7,000 MRBF. It is not as reliable as some very heavy older designs, but it is for its mass.
A similar version of the M240, the M240G (referred to as the "240 Golf"), is the standard U.S. Marine Corps medium machine gun. Following acceptance of the M240E1 for use on the M1 Abrams tank, the Marine Corps traded their M60E3 to the Army for a similar number of M240s. They put the standard infantry trigger group on them, and designated this as the M240G, bypassing the standard, years-long procurement process, and avoiding budgetary problems for the Marine Corps.
This, in turn, made it easier for the Army and Air Force to adopt the M240 in an infantry / dismounted role. As a result, the M60 is in the process of being phased out throughout the US Armed Forces, and has primarily been relegated to use by Reserve and Guard units until they can be completely obsoleted.
The M240 allows for commonality throughout the Marine Corps whether the weapon is used in an infantry, vehicular, or airborne role. The M240G is the ground version of the original M240 or M240E1, 7.62 mm medium class weapon designed as a coaxial/pintle mounted machine gun for Tanks and LAVs. The M240G can be modified for ground use by the installation of an "infantry modification kit," (a flash suppressor, front sight, carrying handle for the barrel, a buttstock, infantry length pistol grip, bipod, and rear sight assembly). The 240G lacks a front heat guard, and is few pounds lighter at 24.2 pounds, than the M240B.