M249 Squad Automatic Weapon (SAW)
The M249 Squad Automatic Weapon (SAW) is one of the main “small” arms weapons used by the soldiers of the United States Army. Officially designated as the M249 light machine gun (LMG), references to the SAW are formally written as Light Machine Gun, 5.56 mm. It was adapted from a Belgian weapon known as the FN Minimi. The FN Minimi is a light machine gun manufactured by FN Herstal (FN). It’s also manufactured by the same company. Introduced in 1984, this is the weapon that provides infantry squads with the high rate of fire of a machine gun while simultaneously proving accuracy and portability nearing that of a rifle.
M249 Operation
The M249 is gas operated and air-cooled. When fired, a portion of the high-pressure gas from the discharging cartridge is used to power a mechanism to dispose of the spent case and insert a new cartridge into the chamber. In that it is air-cooled, it relies solely on the ambient air to dissipate the heat that builds up within the chamber and along the length of the barrel. It features a quick-change barrel, allowing the gunner to replace an overheated or jammed barrel in a matter of seconds. There is a folding bipod attached near the front of the gun. In addition the SAW can be mounted on an M192 LGM tripod for stationary firing.
There are 7 steps to the cycle of functioning for the M249.
- Feeding
- Chambering
- Locking
- Firing
- Unlocking
- Extracting
- Cocking
The M249 can be fed from both linked ammunition and STANAG magazines, like those used in the M16 and M4. WIth linked ammunition, a belt retains and feeds individual cartridges into it minimizing the proportional weight of the ammunition to the weapon system and allowing high rates of continuous fire. The STANAG magazine or NATO magazine is the same detachable magazine used by the rifles allow squad members to easily share 5.56x45mm ammunition within the squad or platoon. Other soldiers can resupply the SAW gunner but it should be noted that the magazines should only be used in emergencies due to the high rate of malfunctions.
M249 Specifications
The M249 is highly portable and is capable of engaging point targets out to a range of 800 meters. It fills a crucial role in the infantry squad along with other combat elements. The specifications for the weapon are as follows:
- CALIBER: 5.56x45mm
- OPERATION: Open-bolt
- WEIGHT: 17 lb.
- BARREL LENGTH: 20.5”
- OVERALL LENGTH: 40.75”
- OVERALL HEIGHT: 9.5”
- RATE OF FIRE: 775 RPM
- EFFECTIVE RANGE: 800m, point target
- MAXIMUM RANGE: 3600m
- TWIST RATE: 1:7″
- TRIGGER PULL: 7.9 lb.
- COLOR: Matte black non-reflective finish
The Implications of the M249 Specifications
Caliber
The 249 uses the standard 5.56×45mm NATO (North Atlantic Treaty Organization) round. This round is of a rimless bottlenecked intermediate cartridge family developed in the late 1970s in Belgium by FN Herstal. The 5.56×45mm NATO cartridge family was derived from and similar in dimensions to the .223, but is not totally identical to the .223 Remington cartridge designed by Remington Arms in the early 1960s.
Operation
When ready to fire, the M249s bolt and working parts are held to the rear of the receiver, with no round in the chamber. When the trigger is actuated, the bolt travels forward, feeds a cartridge from the belt (or magazine) into the chamber, and fires that cartridge in the same movement. Like any other self-loading design, the action is cycled by the gas expended from the round and is sent back to the rear, ejecting the empty cartridge case and preparing for the next shot. (or continuing forward again, if the trigger is held down, the bolt continues forward again in automatic action.
Weight, Length and Height
At 17lbs, the M249 doesn’t become a burden to the combat soldier that has to move, often on foot, around the battlefield. With supplies, ammunition, and other gear, the last thing that the combat soldier needs is a weapon that is heavier than it needs to be! With an overall length of 40.75” and overall height of just 9.5” the weapon lends itself positively to the ability of the soldier to, not only move, but to also take up a solid position with cover and concealment. The SAW is suitable for action in close contact and urban situations.
Barrel Length
A longer barrel has two advantages:
- You get more velocity from the same cartridge, therefore shooting flatter and doing more damage to the target, all else equal.
- If you have iron sights mounted on the barrel, the sights will be further apart, helping you to shoot more accurately.
A shorter barrel has three advantages:
- The gun will be lighter, all else equal.
- The gun will be more maneuverable and easier to store, all else equal.
- The gun will be more concealable
The M249 combines all of these advantages with a medium length barrel.
Rate of Fire
The rates of fire for the M249 are as follows:
- Sustained rate is 100 rounds per minute
- Rapid rate is 200 rounds per minute
- Cyclic rate is 650 to 850 rounds per minute
The sustained rate of the M249 allows for steady fires (sustained) without overheating the barrel or causing other heat induced malfunctions. Typically, this will allow for adequate suppressive fires. In other words, it’s enough to keep the enemy occupied. The rapid rate of fire (between cyclic and sustained) provides faster less accurate fire and is usually only used in final defensive line situations. The cyclic rate, however, allows the weapon to fire as fast as it possibly can. Sustained fire at the cyclic rate will quickly result in an overheating barrel of the air-cooled SAW.
Range
The maximum range of the M249 Squad Automatic Weapon is 3600m while the effective range is 800m. As with all weapons, the effective range is the range in which you can reasonably expect to hit the “point target” at which you are aiming. On the other hand, the maximum range is the total distance that a round fired from the weapon can travel. The main difference between the two is accuracy.
Twist Rate
For best performance, a barrel should have a twist rate great enough to spin stabilize any round that it is expected to fire, but not much more. Like the M16A2 and M4 rifles, the M249 has a 1 in 7-inch (18 cm) or 32 calibers twist. Essentially, the stability of the rounds and thus the accuracy is equal to that of the rifles as a result.
Trigger Pull
Trigger pull is a measurement that is used in determining the level of force it takes to discharge a particular firearm. The trigger pull varies depending on the type of weapon. Typically, the trigger pull weight should be no more than half the weight of the weapon. On the M249, the trigger pull starts at 7.9lbs. At a weight of 17lbs, the amount of pull required falls well below the recommended maximum.
Color
The matte black non-reflective finish of the M249 is consistent with the United States Army standard for firearms. It lends itself to the concealment usually required on the modern-day battlefield.
M249 Ammunition Variants
In combat, the ammunition mix for the M249 is a four-ball (M855) and one-tracer (M856) mix. This will allow the gunner to guide the rounds onto the target by observing the path of the tracers rather than by using the optics. This technique is especially helpful during night engagements. There are, however, other variations of 5.56-mm ammunition available. They are listed in the following table.
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