Military

CHAPTER 1

M249 MACHINE GUN

The 5.56-mm M249 machine gun supports the soldier in both the offense and defense. The M249 provides a medium volume of close and continuous fire the soldier needs to accomplish the mission. With it, units can engage the enemy along with the capability of individual weapons with controlled and accurate fire. The medium-range, close defensive, and final protective fires delivered by the M249 MG form an integral part of a unit's defensive fires. Although the M249 MG is described here as a machine gun, it also plays the role of the automatic rifleman. This FM or chapter supersedes FM 23-14, which describes the M249 MG in the automatic rifle role. This chapter also describes the weapon and the types of ammunition in detail and provides a table of general data.

Section I. DESCRIPTION AND COMPONENTS

This section describes the M249 machine gun and its components and purposes. It also discusses the different types of ammunition that is fired from the M249 machine gun. This section describes how to install the blank firing adapter for the M249 machine gun and how to take care of the machine gun while using the blank firing adapter.

1-1.   DESCRIPTION

The M249 machine gun is a gas-operated, air-cooled, belt or magazine-fed, automatic weapon that fires from the open-bolt position (Figure 1-1). It has a maximum rate of fire of 850 rounds per minute. Primarily, ammunition is fed into the weapon from a 200-round ammunition box containing a disintegrating metallic split-link belt. As an emergency means of feeding, the M249 machine gun can use a 20- or 30-round M16 rifle magazine but increases the chance of stoppages. This gun can be fired from the shoulder, hip, or underarm position; from the bipod-steadied position; or from the tripod-mounted position. See Table 1-1, for general data.

Figure 1-1. M249 machine gun, bipod and tripod mounted.

Figure 1-1.  M249 machine gun, bipod and tripod mounted.

Table 1-1. General data.

Table 1-1.   General data.

1-2.   COMPONENTS

The components of the M249 machine gun and their purposes are described in Table 1-2 and shown Figure 1-2. The item numbers in Table 1-2 correspond to the callout numbers in Figure 1-2. The sights and safety button are shown in Figures 1-3 and 1-4. (See Table 1-1 for general data.)

COMPONENTS

PURPOSES

(1)

Barrel assembly

Houses cartridges for firing, directs projectile, and supports the gas regulator.
 

(2)

Heat shield assembly

Provides protection for the gunner's hand from a hot barrel.
 

(3)

Rear sight assembly

Adjusts for both windage and elevation.
 

(4)

Cover and feed mechanism assembly

Feeds linked belt ammunition, and positions and holds cartridges in position for stripping, feeding, and chambering.
 

(5)

Feed tray assembly

Positions belted ammunition for firing.
 

(6)

Cocking handle assembly

Pulls the moving parts rearward. Moves in a guide rail fixed to the right side of the receiver.
 

(7)

Buttstock and buffer assembly

Contains a folding buttplate. Serves as a shoulder support for aiming and firing M249. Contains a folding shoulder rest and a hydraulic buffer to absorb the recoil.
 

(8)

Bolt assembly

Provides feeding, stripping, chambering, firing, and extraction, using the projectile gases for power.
 

(9)

Slide assembly

Houses firing pin and roller assembly.
 

(10)

Return rod and transfer mechanism assembly

Absorbs recoil for bolt and operating rod assembly at the end of recoil movement.
 

(11)

Receiver assembly

Serves as a support for all major components and houses action of weapon. Through a series of cam ways, controls functioning of weapon.
 

(12)

Trigger mechanism

Controls the firing of the weapon. Provides storage area for lubricant in grip portion.
 

(13)

Handguard assembly

Provides thermal insulation to protect the gunner's hand from heat or extreme cold and houses the cleaning equipment.
 

(14)

Sling and snap hook assembly

Provides a means of carrying the weapon.
 

(15)

Bipod

Supports the M249 machine gun in the prone position. The telescopic legs can be individually adjusted to three different lengths.
 

(16)

Gas cylinder assembly

Locks bipod in place and provides passageway for gases.
 

(17)

Piston assembly

Holds the bolt and slide assemblies and houses the return spring.
 

(18)

Return spring

Returns bolt, slide, and piston assemblies to locked position during counterrecoil cycle.
 

(19)

Tripod (M122) (Not shown)

The tripod and T&E mechanism, with pintle, provides a stable mount and permits a higher degree of accuracy and control.
 

(20)

M145 straight telescope (Not shown)

Machine gun optic (MGO) provides target acquisition and identification at greater ranges.
 

Table 1-2.   Components and purposes.

Figure 1-2. M249 machine gun components.

Figure 1-2.   M249 machine gun components.

a.   Sights. The M249 machine gun has a hooded and semifixed front sight (Figure 1-3). The rear sight assembly mounts on the top of the cover and feed mechanism assembly. The elevation knob drum has range settings from 300 meters to 1,000 meters. Range changes are made on the M249 machine gun sight by rotating the elevation knob to the desired range setting. Rotation of the rear sight aperture (peep sight) is used for fine changes in elevation or range adjustments, such as during zeroing. Each click of the peep sight. One click moves the sight 180 degrees, or one-half turn. This equals a one-half-mil change in elevation, which is .5 cm at 10 meters. The sight adjusts for windage by rotating the windage knob. Each click of windage adjustment also equals a one-half-mil change, which is .5 cm at 10 meters. There is also a windage sliding scale marked with index lines for centering the rear sight aperture.

Figure 1-3. Sights

Figure 1-3.   Sights.

b.   Safety. The safety (Figure 1-4) is in the trigger housing. The safety is pushed from left to right (red ring not visible) to render the weapon safe, and the bolt cannot be released to go forward. The safety is pushed from right to left (red ring visible) to render the weapon ready to fire. The cocking handle on the right side of the weapon is used to pull the bolt to the rear.

Figure 1-4. M249 machine gun safety

Figure 1-4.   M249 machine gun safety.

1-3.   AMMUNITION

The M249 machine gun uses several different types of 5.56-mm standard military ammunition. Soldiers should use only authorized ammunition that is manufactured to US and NATO specifications. The 5.56-mm NATO cartridge is identified by its appearance, the painted projectile tips, the stamped manufacturer's initials and year of manufacture on the base of the cartridge case, and the markings on the packing containers. When removed from the original packing container, the cartridge can be identified by its physical characteristics. The M193 and M196 cartridge for the M16 can be fired with the M249, but accuracy is degraded; therefore, it should only be used in emergency situations when M855 or M856 ammunition is not available.

a.   Type and Characteristics. The specific types of ammunition (Figure 1-5) and its characteristics are as follows.

Figure 1-5. Cartridges for the M249.

Figure 1-5.   Cartridges for the M249.

(1)   Cartridge, 5.56-mm ball M855 (A059). The M855 cartridge has a gilding, metal-jacketed, lead alloy core bullet with a steel penetrator. The primer and case are waterproof. This ammunition is linked by a disintegrating metallic split-linked belt so that the ammunition can feed from the ammunition box (Figure 1-6). In an emergency, the M855 round can also be fired from the M16A2, A3, or A4 when loaded in a 20- or 30-round magazine. It is identified by a green tip, has a projectile weight of 62 grains, and is 2.3 cm long. This is the NATO standard round. It is effective against personnel and light materials, not vehicles.

Figure 1-6. M855 cartridges in metallic belt.

Figure 1-6.   M855 cartridges in metallic belt.

(2)   Cartridge, 5.56-mm tracer, M856 (A064). This cartridge has a projectile weight of 63.7 grains and lacks a steel penetrator. It is identified by an orange tip. The tracer is used for adjustments after observation, incendiary effects, and signaling. When tracer rounds are fired, they are mixed with ball ammunition in a ratio of four ball rounds to one tracer round. The DODAC for ball and tracer mix is A064.

(3)   Cartridge, 5.56-mm dummy M199 (A060). This cartridge can be identified by the six grooves along the side of the case beginning about one-half inch from its head. It contains no propellant or primer. The primer well is open to prevent damage to the firing pin. The dummy round is used during mechanical training, dry-fire exercises, and function checks.

NOTE:

The 5.56-mm NATO cartridge may be identified by its appearance, the painting of projectile tips, the stamping of the manufacturer's initials and year of manufacture on the base of the cartridge case, and the markings on the packing containers. When removed from the original packing container, the cartridge can be identified by its physical characteristics. The M193 and M196 cartridge for the M16 can be fired with the M249, but accuracy is degraded; therefore, it should only be used in emergency situations when M855 or M856 ammunition is not available.

(4)   Cartridge, 5.56-mm blank M200 (M2 link, A075). The blank cartridge has no projectile. The case mouth is closed with a seven-petal rosette crimp and has a violet tip. The original M200 blank cartridge had a white tip. Field use of this cartridge resulted in residue buildup, which caused malfunctions. Only the violet-tipped M200 cartridge should be used. The blank round is used during training when simulated live fire is desired. The M249 blank-firing attachment (NSN 1005-21-912-8997) must be used to fire this ammunition. (See paragraph 1-4.)

DANGER
DO NOT FIRE BLANK AMMUNITION AT ANY PERSON WITHIN 20 FEET BECAUSE FRAGMENTS OF A CLOSURE WAD OR PARTICLES OF UNBURNED PROPELLANT CAN CAUSE INJURY OR DEATH.

b.   Storage. Ammunition is stored under cover. If ammunition is in the open, it must be kept at least 6 inches above the ground and covered with a double thickness of tarpaulin. The cover must be placed so that it protects the ammunition yet allows ventilation. Trenches are dug to divert water from flowing under the ammunition.

c.   Care, Handling, and Preservation. Ammunition should not be removed from the airtight containers until ready for use. Ammunition removed from the airtight containers, particularly in damp climates, may corrode.

(1)   Ammunition must be protected from mud, dirt, and moisture. If it gets wet or dirty, the ammunition must be wiped off before use. Lightly corroded cartridges are wiped off as soon as the corrosion is discovered. Heavily corroded, dented, or loose projectiles should not be fired.

(2)   Ammunition must be protected from the direct rays of the sun. Excessive pressure from the heat may cause premature detonation.

(3)   Oil should never be used on ammunition. Oil collects dust and other abrasives that may possibly damage the operating parts of the weapon.

d.   Packaging. The ammunition can contains two plastic ammunition drums. Each drum contains 200 rounds and weighs 6.92 pounds. Dummy ammunition (M199) is packed in boxes of 20 rounds each.

1-4.   BLANK FIRING ATTACHMENT

The M249 BFA is the only BFA (NSN 1005-21-912-8997) authorized for use with the M249 MG.

a.   Installation. The BFA is attached to the M249 machine gun by using the three steps shown in (Figure 1-7).

Figure 1-7. M249 blank firing attachment.

Figure 1-7.   M249 blank firing attachment.

b.   Care of the M249 While Using the BFA. A buildup of carbon inside the weapon causes friction between the moving parts. Carbon deposits build rapidly when blanks are fired. When these deposits become excessive, stoppages occur. Therefore, keeping the weapon-especially the gas system and chamber-clean, during blank firing is very important. To get the best performance with the BFA, the automatic rifleman performs the following:

(1)   Inspects the weapon for damaged parts, excessive wear, cleanliness, and proper lubrication before firing.

(2)   When feasible, test fires the weapon using ball ammunition before attaching the BFA.

(3)   Adjusts the BFA to fit the weapon.

(4)   Applies immediate action when stoppages occur.

(5)   Cleans the gas system after firing 500 rounds.

(6)   Cleans and lubricates the entire weapon after firing 1,000 rounds.

Section II. MAINTENANCE

Proper maintenance contributes to weapon effectiveness as well as to unit readiness. This section discusses the maintenance aspects of the M249 machine gun to include inspection; cleaning and lubrication; maintenance before, during, and after firing, and during NBC conditions. Associated tasks essential to maintenance (clearing, general assembly and disassembly, and function checks) are provided in detail.

1-5.   CLEARING PROCEDURES

The first step in maintenance is to clear the weapon (Figure 1-8). This applies in all situations, not just after firing. The gunner must always assume the M249 machine gun is loaded. To clear the M249, the gunner performs the following procedures:

a.   Moves the safety to the fire "F" position by pushing it to the left until the red ring is visible.

b.   With his right hand, palm up, pulls the cocking handle to the rear, locking the bolt in place.

c.   While holding the resistance on the cocking handle, moves the safety to the SAFE position by pushing it to the right until the red ring is not visible. (The weapon cannot be placed on safe unless the bolt is locked to the rear.)

d.   Returns and locks the cocking handle in the forward position.

DANGER
WHEN OPENING THE FEED COVER ON A HOT GUN, MAKE SURE THE WEAPON IS ON THE GROUND AWAY FROM YOUR FACE. WITH THE WEAPON ON YOUR SHOULDER, POSSIBLE DEATH OR INJURY COULD OCCUR IF A ROUND GOES OFF WHEN THE COVER IS RAISED.

e.   Raises the cover and feed mechanism assembly, and conducts the five-point safety check for brass, links, or ammunition:

(1)   Checks the feed pawl assembly under the feed cover.

(2)   Checks the feed tray assembly.

(3)   Lifts the feed tray assembly and inspects the chamber.

(4)   Checks the space between the bolt assembly and the chamber.

(5)   Inserts two fingers of his left hand in the magazine well to extract any ammunition or brass.

f.   Closes the cover and feed mechanism assembly and moves the safety to the "F" position. With his right hand, palm up, returns the cocking handle to the rear position. Presses the trigger and at the same time eases the bolt forward by manually riding the cocking handle forward.

CAUTION
The cocking handle must be manually returned to the forward and locked position each time the bolt is manually pulled to the rear.

Figure 1-8. Clearing procedures.

Figure 1-8.   Clearing procedures.

Figure 1-8. Clearing procedures (continued).

Figure 1-8.   Clearing procedures (continued).

1-6.   GENERAL DISASSEMBLY

General disassembly is removing and replacing the eight major groups (Figure 1-9). The unit armorer performs detailed disassembly. Disassembly beyond what is explained in this manual is prohibited, except by ordnance personnel. During general disassembly, each part is placed on a clean flat surface such as a table or mat. This aids in assembly in reverse order and avoids the loss of parts. Before disassembly, the bipod legs must be released from under the receiver and placed into the bipod mode position.

DANGER
BE SURE THE BOLT IS IN THE FORWARD POSITION BEFORE DISASSEMBLY. THE GUIDE ROD CAN CAUSE DEATH OR INJURY IF THE GUIDE SPRING IS RETRACTED WITH THE BOLT PULLED TO THE REAR.

Figure 1-9. Eight major groups.

Figure 1-9.   Eight major groups.

a.   Removing the Operating Rod Group. The operating rod group (Figure 1-10), operating rod spring, slide assembly, piston assembly, and bolt assembly consists of the spring guide rod.

(1)   To remove the operating rod, pull the upper retaining pin at the rear of the receiver to the left. Allow the buttstock to pivot downward and place it on a surface to support the weapon for disassembly.

(2)   To release the operating rod assembly from the positioning grooves inside the receiver, hold the weapon with one hand on the buttstock assembly. Use the thumb of the other hand to push in and upward on the rear of the operating rod assembly.

(3)   Pull the operating rod and spring from the receiver group and separate the parts.

(4)   Hold the buttstock assembly with your left hand to stabilize the weapon. With your right hand, pull the cocking handle to the rear to lock the bolt. Return the cocking handle to the forward position. Place a finger on the face of the bolt and push until your finger makes contact with the bridge at the end of the receiver. This leaves the piston, slide, and bolt assemblies exposed.

(5)   Hold the slide assembly while pulling the moving parts out the rear of the receiver. This leaves the piston, slide, and bolt assemblies exposed.

Figure 1-10. Removal of the operating rod group.

Figure 1-10.   Removal of the operating rod group.

(6)   To separate the operating rod group (Figure 1-11), hold the piston assembly in one hand, place your other hand on the bolt assembly, and rotate the bolt to disengage it bolt from the slide assembly. Remove the firing pin spring from the firing pin, but be careful not to break the spring. If the spring sticks, rotate it clockwise to free it. The weapon will function without the spring, but this weakens the firing pin action. To separate the slide assembly from the piston, press the retaining pin at the rear of the slide assembly to the left and lift the slide assembly.

Figure 1-11. Separation of the operating rod group.

Figure 1-11.   Separation of the operating rod group.

b.   Removing the Barrel Group. The barrel group consists of barrel, heat shield, flash suppressor, front sight, gas regulator, and gas regulator collar. The following steps correspond to the callouts in Figure 1-12.

CAUTION
Barrels must not be interchanged with those from other M249s unless the headspace has been certified for that weapon by direct support personnel.

(1)   To remove the barrel from the receiver, close the cover and feed mechanism assembly. Depress the barrel locking lever with your left hand, then lift the carrying handle using your right hand and push the barrel forward. To remove the heat shield, place the barrel with the muzzle end on a hard, flat surface, with the heat shield facing away from your body. Place the index fingers of each hand inside the chamber. Use your thumbs to push up on the top clip.

Figure 1-12. Removal of the barrel.

Figure 1-12.   Removal of the barrel.

(2)   Raise the feed cover.

(3)   To remove the gas regulator and collar, rotate the gas collar pin out of the notch. Place the tip of the scraper with the concave side facing the pin of the collar inside the notch. (Be careful not to use too much pressure, so as not to break the tip of the scraper.) Rotate the collar counterclockwise over the concave portion of the tip, which is on the scraper, and past the notch until the collar slides off (Figure 1-13). Deficiencies that are not correctable by the operator must be reported to the squad leader or NCOIC.

NOTE:

The newest style barrel has an internal gas system, which cannot be disassembled.

Figure 1-13. Removal of the collar.

Figure 1-13.   Removal of the collar.

(5)   To remove the gas regulator (Figure 1-14), separate it from the gas block.

Figure 1-14. Removal of the gas regulator.

Figure 1-14.   Removal of the gas regulator.

c.   Removing the Handguard Group. The handguard group (Figure 1-15) consists of the handguard, handguard retaining pin, and cleaning equipment retaining clip. Push the handguard retaining pin to the left using a cartridge or the spring guide rod; then pull the handguard down.

Figure 1-15. Removal of the handguard.

Figure 1-15.   Removal of the handguard.

CAUTION
Do not attempt to remove the handguard retaining pin completely. It is a captured pin.

d.   Removing the Buttstock and Buffer Assembly Group. To remove the buttstock and buffer assembly (Figure 1-16), use a cartridge or the spring guide rod to push the lowermost retaining pin on the rear of the receiver to the left. It is a captured pin; it is not removable. Remove the buttstock and shoulder assembly by pulling them rearward, while supporting the trigger mechanism.

Figure 1-16. Removal of the buttstock and buffer assembly.

Figure 1-16.   Removal of the buttstock and buffer assembly.

e.   Removing the Trigger Mechanism Group. After the release of the support, the trigger mechanism will automatically be removed because the lowermost retaining pin holds it on.

f.   Removing the Gas Cylinder Group. To remove the gas cylinder from the receiver (Figure 1-17), grasp the gas cylinder at the top of the bipod legs, turn it to the left or right to release the locking spring, and then pull it away from receiver.

CAUTION
Do not attempt to remove the upper and lower retaining pins completely. They are captured pins.

Figure 1-17. Removal of the gas cylinder group.

Figure 1-17.   Removal of the gas cylinder group.

g.   Removing the Bipod Group. Once the gas cylinder group is removed, remove the bipod group (Figure 1-18) by pulling it away from the receiver.

Figure 1-18. Removal of the bipod group.

Figure 1-18. Removal of the bipod group.

h.   Removing the Receiver Group. Once the bipod group is removed, the part remaining is the receiver group, and disassembly is complete.

1-7.   INSPECTION

Inspection begins with the weapon disassembled in its major groups. Shiny surfaces do not mean the parts are unserviceable. The parts of the weapon and related equipment are inspected. Any broken or missing parts are repaired or replaced IAW TM 9-1005-201-10. The gunner performs preventive maintenance checks and services (PMCS) every 90 days. If the weapon has not been used in 90 days, PMCS is performed as stated in the operator's manual. If rust is seen on the weapon, perform PMCS immediately:

a.   Operating Rod Group. The operating rod should not be bent, broken, or cracked. The buffer spring should not have breaks. Lug pins should protrude equally on both sides of the buffer spacer. The operating rod spring should not have kinks or separated strands or broken strands. It can have a maximum of one break on any one strand.

(1)   Check the bolt assembly for visible damage. The cartridge extractor should not be cracked or chipped.

(2)   Check the slide assembly for visible damage. Check the feed roller for spring tension when compressed and to ensure that the pivot slide is locked onto the slide assembly.

(3)   Check the firing pin for straightness and cracks. Ensure the tip is completely rounded.

(4)   Ensure the firing pin spring is not crushed or bent. Ensure the beveled end is not stretched.

(5)   Check the sear notch on the piston assembly for signs of excessive wear or burring. Slight rotation of the piston on its housing is normal and is not cause for rejection.

b.   Barrel Group. The flash suppressor should not be cracked, and it should be fastened securely. The front sight post and front sight base must not be bent, cracked, or broken. Weapons already zeroed should not be adjusted. The heat shield assembly is inspected for damage, cracks, or broken retaining clamps. The gas regulator and collar are checked for cracks or burrs. The barrel is checked for bulges, cracks, bends, obstructions, or pits in the chamber or bore. The gas plug is checked for obstructions, cracks, and bulges. The carrying handle is checked to ensure it is not cracked, broken, or missing; that it can be folded under spring pressure to the right and left; and that it remains locked in an upright position.

c.   Handguard Group. The handguard should not be cracked or broken. The retaining clip must be attached to the handguard retaining pin.

d.   Buttstock and Buffer Assembly Group. The buttstock is checked for cracks, bends, or breaks; and for missing components. It is checked for linkage and tension on the buffer rod. The shoulder rest is checked to ensure it is not bent or broken and that it locks in both positions.

e.   Trigger Mechanism Group. The shoulder of the sear should not show excessive wear. The safety should function properly. That is, the sear should move only slightly when the safety is on "S" and freely when the safety is on "F". The sear pin should not protrude from the trigger mechanism, because, if it does protrude, the trigger mechanism will not go back in place.

f.   Gas Cylinder Group. The gas cylinder should not be cracked, bent, or broken.

g.   Bipod Group. The bipod group should not be cracked, bent, or broken. The bipod legs should extend and collapse easily.

h.   Receiver Group. The cover latch should work properly. All parts inside the cover assembly should move under spring tension. All spotwelds are checked for cracks. The cover assembly should remain open without support. The belt-holding pawl must be under spring tension. The receiver should not be bent or cracked. The cocking handle should slide freely within its guide and lock in its forward position. The windage and elevation knobs on the rear sight should be movable and legible. The windage scale screws should not be worn or burred.

1-8.   CLEANING, LUBRICATION, AND PREVENTIVE MAINTENANCE

The M249 machine gun should be cleaned immediately after firing. It should be disassembled into its major groups before cleaning. After it has been cleaned and wiped dry, a thin coat of CLP is applied by rubbing with a cloth. This lubricates and preserves the exposed metal parts during all normal temperature ranges. When not in use, the M249 should be inspected weekly and cleaned and lubricated when necessary.

a.   Cleaning. All metal components and surfaces that have been exposed to powder fouling should be cleaned using CLP on a bore-cleaning patch. The same procedure is used to clean the receiver.

CAUTION
When using CLP, no other type cleaner can be used. Never mix CLP with RBC or LSA.

(1)   Clear and disassemble the weapon.

(2)   Clean the bore and chamber using CLP and fresh swabs.

(3)   Clean the gas regulator with the special tool (scraper). Remove all carbon dust. Do not use CLP on the collar, gas block, or body.

(a)   Clean the gas-vent hole (Figure 1-19).

Figure 1-19. Cleaning of the gas vent hole.

Figure 1-19.   Cleaning of the gas vent hole.

(b) Clean the central hole with the appropriate part of the scraper by turning it clockwise and pushing it inward toward the bottom of the housing (Figure 1-20).

Figure 1-20. Cleaning of the central hole.

Figure 1-20.   Cleaning of the central hole.

(c)   Use the protruding tips of the scraper to clean the two grooves of the body (Figure 1-21).

Figure 1-21. Cleaning of the grooves of the body.

Figure 1-21.   Cleaning of the grooves of the body.

(4)   Clean the gas cylinder and piston with the special tool (scraper). Do not use CLP on the gas cylinder or piston.

(a)   Clean the front interior of the gas cylinder (repositioned in receiver with bipod in place) by inserting and turning the flat side of the scraper in a 360-degree circular motion (Figure 1-22).

(b)   Clean the internal grooves of the front side of the gas cylinder the same as, except insert the scraper farther into the gas cylinder (Figure 1-22).

Figure 1-22. Cleaning of the front interior and internal grooves of the gas cylinder.

Figure 1-22.   Cleaning of the front interior and internal
grooves of the gas cylinder.

(c)   Clean the three grooves of the piston using a 360-degree circular motion (Figure 1-23). Remove all carbon dust from the piston, inside and out.

Figure 1-23. Cleaning of the grooves of the piston.

Figure 1-23.   Cleaning of the grooves of the piston.

(d)   Clean the hole in the front of the piston by inserting and turning the flat side of the scraper in a 360-degree circular motion (Figure 1-24).

Figure 1-24. Cleaning of the hole in the front of the piston.

Figure 1-24.   Cleaning of the hole in the front of the piston.

(5)   Clean carbon and dirt from all other parts of the weapon.

(6)   A cloth saturated in CLP is used on exterior surfaces to prevent corrosion.

b.   Lubrication. After the M249 machine gun is cleaned and wiped dry, a thin coat of CLP is applied by rubbing it on with a cloth. This lubricates and preserves the exposed metal parts during all normal temperature ranges. The moving parts are also lubricated with CLP. After lubricating, the components are rubbed by hand to spread the CLP.

(1)   Operating rod group. Use CLP on the operating rod and spring, the slide assembly, the feed roller, and the bolt-locking lug.

(2)   Barrel group. Use CLP on the cam surfaces of the bolt-locking lugs, the heat shield, and along the outer surfaces of the barrel clamp.

(3)   Receiver group. Use CLP on all moving parts on the cover assembly and the receiver rails.

c.   Preventive Maintenance. Weapons that are seldom fired or stored for prolonged periods should have a light film of CLP applied to the interior of the gas plug, the gas regulator, and the piston immediately after cleaning or inspecting. Preventive maintenance is performed every 90 days, unless inspection reveals more frequent servicing is necessary. The use of the lubricant does not eliminate the need for cleaning and inspecting to ensure that corrosion has not formed. The gas regulator, gas plug, and piston must be clean and free of oil and lubricants before using the weapon. If it is not clean and oil free, stoppages will occur. CLP is the only lubricant to use on the M249 machine gun. The following procedures apply to cleaning and lubricating the M249 machine gun during unusual conditions:

(1)   Extremely hot— use CLP, grade 2.

(2)   Damp or salty air— use CLP, grade 2. Clean and apply frequently.

(3)   Sandy or dusty areas— use CLP, grade 2. Clean and apply frequently. Remove excess with a rag after each application.

(4)   Below -18 degrees Celsius (0 degrees Fahrenheit) — use CLP, grade 2, generously. Lubricate heavily enough so that the lubricant can be spread with finger. Although CLP provides required lubrication at temperatures between 0 degrees Fahrenheit and -35 degrees Fahrenheit, it will not flow from a 1/2-ounce bottle at temperatures below 0 degrees Fahrenheit.

1-9.   GENERAL ASSEMBLY

The M249 machine gun is assembled in reverse order of the disassembly.

a.   Replacing the Receiver Group and Bipod Group. Place the bipod group on the receiver group with the bipod legs open and pointed downward. (See Figure 1-18.)

b.   Replacing the Gas Cylinder Group. Push the gas cylinder through the bipod yoke into the receiver. Push the cylinder to the rear while countering the pressure of the locking spring and guiding the end of the cylinder into the receiver with the other hand applying downward pressure. Position the recess in the cylinder near the spring. Turn the cylinder until the spring clicks into the recess at the rear of the gas cylinder (Figure 1-25).

Figure 1-25. Replacement of gas cylinder group.

Figure 1-25.   Replacement of gas cylinder group.

c.   Replacing the Trigger Mechanism Group. Align the trigger mechanism (Figure 1-26) with the slot on the bottom of the receiver. Hold the trigger mechanism in position to accomplish the next step.

Figure 1-26. Replacement of the trigger mechanism group.

Figure 1-26.   Replacement of the trigger mechanism group.

d.   Replacing the Buttstock and Buffer Assembly Group. Align the lower hole in the buttstock and buffer assembly with the rear hole in the trigger mechanism; then push the lower retaining pin to the right (Figure 1-27).

Figure 1-27. Replacement of the buttstock and buffer assembly group.

Figure 1-27.   Replacement of the buttstock and buffer assembly group.

e.   Replacing the Handguard Group. To replace the handguard (Figure 1-15), place it on the receiver from the bottom and push it to the rear until it stops. Using the guide rod, push the handguard retaining pin to the right, which locks the handguard into position. Push the handguard down to make sure it is locked.

f.   Replacing the Barrel Group. Insert the gas regulator into the gas block and align the notch on the gas regulator with the notch of the gas block. With the gas regulator already installed and supported on a firm surface, place the gas regulator collar onto the protruding end of the body and align the spring with the stud. Push the gas regulator collar downward firmly and rotate it until it slips into place. Then, press it in and rotate it to lock it in place. Depress the barrel locking lever to the rear with your left hand, while holding the carrying handle with your right hand. Pull the barrel rearward and push downward; align the gas regulator with the gas cylinder and lock it by releasing the barrel locking lever. Check the barrel to ensure it is locked into the receiver by pulling or lifting on the carrying handle. Replace the heat shield by placing the hook end of the heat shield under the front sight post and press down until the clamps lock on the barrel. (Figure 1-28).

Figure 1-28. Replacement of the barrel group.

Figure 1-28.   Replacement of the barrel group.

g.   Replacing the Operating Rod Group. Hold the piston in one hand with the face of the piston facing outward and the sear notches downward. With the other hand, place the slide assembly onto the rear of the piston with the firing pin toward the front of the piston. (Check the slide assembly retaining pin to make sure it is out.) (Figure 1-29).

(1)   Push the slide assembly retaining pin to the right. This locks together the piston assembly and the slide assembly.

(2)   Put the firing pin spring on the firing pin of the slide assembly. Place the bolt on the slide assembly, aligning the driving lug of the bolt with the slot of the slide assembly. Apply pressure to the face of the bolt to compress the firing pin spring. Then, rotate the bolt to hook the driving lug into the slide assembly. Open the cover assembly on the receiver. Insert the face of the piston into the receiver, aligning the bolt lugs onto the receiver rails. Pull the trigger and push the moving parts forward until the bolt is seated into the chamber.

(3)   Place the operating rod tip into the operating rod spring. Then, insert the free end of the operating rod and spring into the rear of the piston. Depress the rear of the operating rod assembly until the two lugs on the buffer are positioned in the receiver grooves.

(4)   Pivot the buttstock upward into position and push the upper retaining pin to the right, locking the buttstock to the receiver.

Figure 1-29. Replacement of the operating rod group.

Figure 1-29.   Replacement of the operating rod group.

1-10.   FUNCTION CHECK

A function check must be performed to ensure that the M249 machine gun has been assembled correctly. The procedures, in order, are as follows:

a.   Grasp the cocking handle with the right hand, palm up, and pull the bolt to the rear, locking it in place.

b.   While continuing to hold the resistance on the cocking handle, use the left hand to move the safety to the SAFE position.

c.   Push the cocking handle forward into the forward lock position.

d.   Pull the trigger (The weapon should not fire).

e.   Grasp the cocking handle with the right hand, palm up, and pull and hold it to the rear.

f.   Move the safety to the FIRE position.

g.   While continuing to hold resistance on the cocking handle, use the left hand to pull the trigger and ease the bolt forward to prevent it from slamming into the chamber area and damaging the face of the bolt.

h.   If the weapon fails the function check, check for missing parts or repeat the reassembly procedures. Before disassembling the weapon, make sure it is positioned where the guide rod and spring cannot cause bodily harm if the bolt is locked to the rear. The cover and feed mechanism assembly can be closed with the bolt in either the forward or the rearward position.

CAUTION
Ease the bolt forward to prevent damage to the hardened surfaces on the bolt, barrel, and so forth.

1-11.   MAINTENANCE PROCEDURES

There are certain actions that must be taken before, during, and after firing to properly maintain the M249 machine gun.

a.   Before firing—

(1)   Wipe the bore dry.

(2)   Inspect the weapon as outlined in the operator's TM.

(3)   Lubricate the weapon.

b.   During firing—

(1)   Inspect the weapon periodically to ensure that it remains lubricated.

(2)   When malfunctions or stoppages occur, follow the procedures in Section IV.

c.   After firing—

(1)   Immediately clear and clean the weapon.

(2)   Every 90 days during inactivity, clean and lubricate the weapon, unless inspection reveals more frequent servicing is necessary.

1-12   MAINTENANCE DURING NUCLEAR, BIOLOGICAL, CHEMICALCONDITIONS

If the M249 machine gun is contaminated by chemical, biological, or radiological agents, the appropriate action must be taken to reduce exposure and penetration.

a.   Chemical. Use towelettes from the M258A1 kit to wipe off the weapon. If these are not available, wash the weapon with hot, soapy water, and rinse.

b.   Biological. Use towelettes or hot, soapy water and rinse the weapon as above.

c.   Radiological. Brush or wipe the weapon, or wash with water, and rinse. For more details, see FM 3-5.

Section III. OPERATION AND FUNCTION

This section discusses the operation and function of the M249 machine gun. They include loading, firing, unloading, cycle of functioning, adjusting the sight, and using the bipod.

1-13.   OPERATION

The M249 machine gun operations are loading, firing, unloading, and using belted ammunition or, in an emergency, a 20- or 30-round M16 magazine. The firing operation works on gas pressure created as a fired round passes through the barrel. The M249 is loaded, fired, unloaded, and cleared from the open-bolt position. The safety must be in the FIRE position before the bolt can be pulled to the rear. Before using belted ammunition, it must be checked to ensure it is properly linked with the double link or the link tab at the open end of the box. It must be free of dirt and corrosion. When using a magazine of ammunition, it must be loaded into the magazine well and be free of dirt and corrosion.

1-14.   LOADING

To load the M249, the weapon must be cleared as described. (With the feed cover raised, the gunner makes sure his face is not exposed to the open chamber area while loading.) (Figure 1-30).

Figure 1-30. Loading.

Figure 1-30.   Loading.

a.   Belt. When loading belted ammunition (Figure 1-31), always cant the weapon to the right. Make sure the open side of the links is facing down, and place the lead link tab or first round of the belt in the tray groove against the cartridge stop. The rounds should be placed flat across the feed tray. With your left hand, count five to six rounds down to hold ammunition in place on the feed tray, while at the same time closing the feed cover with your right hand. When closing the feed cover, always place your hand in front of the rear sight to prevent accidentally changing the sight adjustment.

Figure 1-31. Belt-fed ammunition.

Figure 1-31.   Belt-fed ammunition.

NOTE:

Use the 20- or 30-round magazine for emergency use only when linked ammunition is not available.

b.   Magazine. Load the 20- or 30-round magazine by inserting it into the magazine well on the left side of the receiver. Push the magazine firmly into the well until it seats and the release tab clicks into the recess on the magazine (Figure 1-32).

Figure 1-32. Loading of a magazine.

Figure 1-32.   Loading of a magazine.

1-15.   UNLOADING

To unload the weapon, pull the bolt and, if it is not already locked lock it in the rear position, it is locked there at this time. The safety is placed on "S". Depending on whether belt-fed or magazine-fed ammunition is used, the following procedures are used:

WARNING
With a hot gun, before you raise the feed cover, move the weapon away from your face so that you are not exposed to the open chamber.

a.   Belt. Raise the feed cover and remove any ammunition or links from the feed tray. Perform the five-point safety check.

b.   Magazine. Push the magazine release tab down and pull the magazine from the magazine well. Raise the feed cover and perform the five-point safety check.

1-16.   CYCLE OF FUNCTIONING

The gunners can recognize and correct stoppages when they know how the M249 machine gun functions. The weapon functions automatically as long as ammunition is fed into it, and the trigger is held to the rear. Each time a round is fired the parts of the weapon function in a cycle or sequence. Many of the actions occur at the same time. These actions are separated in this manual only for instructional purposes.

a.   The cycle is started by putting the first round of the belt in the tray groove or by inserting the magazine into the magazine well. Then the trigger is pulled, releasing the sear from the sear notch. When the trigger is pulled to the rear, the rear of the sear is lowered and disengaged from the sear notch. This procedure allows the piston and bolt to be driven forward by the expansion of the operating rod spring. The cycle stops when the trigger is released and the sear again engages the sear notch on the piston.

b.   The sequence of functioning is as follows:

(1)   Feeding. As the bolt starts its forward movement, the feed lever is forced to the right, causing the feed-pawl assembly to turn in the opposite direction. This forces the feed-pawl assembly over the next round in the belt, and the feed-pawl assembly is ready to place the next round into the tray groove when the rearward action occurs again. As the bolt moves to the rear after firing, the feed roller forces the feed lever to the left. The feed lever is forced to turn, moving the feed pawl to the right. This places a round in the tray groove.

(2)   Chambering. As the bolt travels forward, the upper stripping (belt-fed or magazine-fed) lug engages the rim of the round. The pressure of the front and rear cartridge guides holds the round so that a positive contact is made with the upper stripping lug of the bolt. The front cartridge guide prevents forward movement of the link as the round is stripped from the belt. The upper locking lug carries the round forward. The chambering ramp causes the nose of the round to be cammed downward into the chamber. When the round is fully seated in the chamber, the extractor snaps over the rim of the round, and the ejector on the rail inside the receiver is depressed.

(3)   Locking. As the round is chambered, the bolt enters the barrel socket. The upper and lower locking lugs contact the bolt camming surfaces inside the barrel and start the bolt turning clockwise. The action of the bolt into the slide assembly, as the piston continues forward, turns the bolt to complete its 90-degree (one-quarter turn) clockwise rotation. Locking is now complete.

(4)   Firing. After the bolt is fully forward and locked, the piston continues to go forward independently of the bolt for a short distance. The piston assembly carries the firing pin through the face of the bolt. The firing pin strikes the primer of the round, and the primer fires the round.

(5)   Unlocking. After the round is fired and the bullet passes the gas port, part of the expanding gases go into one block (new style) or into the gas regulator through the gas plug. The rapidly expanding gases enter into the gas cylinder from the gas regulator, forcing the piston to the rear. As the piston continues to the rear, the slide assembly's simultaneous movement to the rear causes the bolt to begin its counterclockwise rotation. The upper and lower locking lugs of the bolt contact the bolt camming surfaces inside the barrel socket and, as the bolt continues toward the rear, it completes a one-quarter turn counterclockwise. The rotation and movement to the rear unlocks the bolt from the barrel socket.

(6)   Extracting. Extracting begins during the unlocking cycle. The rotation of the bolt loosens the cartridge case in the chamber. As the piston and bolt move to the rear, the extractor pulls the cartridge case from the chamber.

(7)   Ejecting. As the cartridge case is pulled from the chamber, the bolt passes by the ejector. This procedure causes the ejector clip to expand, forcing the ejector to push the expended cartridge. The extractor grips the right side of the cartridge and causes it to spin from the weapon as it reaches the ejection port. The empty belt links are forced out of the link ejection port as the rearward movement of the bolt causes the next round to be positioned in the tray groove.

(8)   Cocking. The piston assembly acts against the firing pin, pulling the firing pin from the primer of the spent cartridge case. The action of the piston assembly, continuing to the rear with the firing pin, releases the compression of the firing pin spring. As long as the trigger is held to the rear, the M249 will continue to complete the eight steps of functioning automatically. When the trigger is released and the sear again engages the sear notch, the cycle of functioning is stopped and the weapon is cocked. To prevent undue wear to the sear and sear notch, the automatic rifleman must hold the trigger firmly to the rear during firing.

1-17.   SIGHTS

This paragraph provides information on how to set the sights for elevation and windage for the M249 machine gun. It also includes information on how to make corrections if the initial setting on the windage knob or peep sight is not accurate. On a 10-meter target, each paster is 1 cm. Therefore, two clicks on the windage knob in either direction moves the strike of the round left or right 1 cm, and two turns on the peep sight moves the strike of the round up or down 1 cm. For example, if the shot group was 2 cm above and 1 cm to the right of the paster, sight corrections are made first by correcting the windage. In this case, the windage knob is rotated two clicks toward the buttstock (clockwise). The elevation knob is rotated four turns toward the buttstock (clockwise) to lower the strike of the round. (See Figure 1-33, below and Table 1-3.)

Figure 1-33. Sliding scale on sight.

Figure 1-33.   Sliding scale on sight.

a.   Elevation. Adjustments for elevation (range) require the automatic rifleman to turn the elevation knob (closest to the buttstock) on the rear sight to the desired range setting. Range settings are graduated increments from 300 to 1,000 meters. Even-numbered settings are on the left side of the scale wheel and are numbered 4, 6, 8, 10, which represent 400, 600, 800, and 1,000 meters, respectively. Odd-numbered settings are on the right side of the scale wheel and marked with the number 3 and three index lines, which represent 300, 500, 700, and 900 meters, respectively. Rotation of the elevation knob toward the muzzle (counterclockwise) increases the range, while rotation toward the buttstock (clockwise) decreases the range. Fine adjustments, like zeroing, are made by adjusting the peep sight. Each 180-degree turn equals a half-mil change in elevation, which equals a half-cm change in impact at a range of 10 meters. Clockwise (to the right) rotations decrease elevation, while counterclockwise (to the left) rotations increase elevation. The peep sight can be turned nine 180-degree turns from top to bottom. To make the peep sight easier to grasp, the elevation knob is turned to its highest point (1,000 meters). The appropriate adjustment is made for the peep sight, and then the sight is returned to the desired range. Whenever readjusting the range, the point of aim is never changed. The point of aim is the center base of the target.

b.   Windage. Adjustments for windage are made by traversing the rear sight right and left along the sliding scale. The sliding scale is marked or graduated with index lines. Each index line is equal to a half-mil change in direction or a half-cm change of impact at 10 meters. Rotation of the windage knob (closest to the muzzle end) toward the muzzle (counterclockwise) moves the rear sight aperture right, which moves the strike of the rounds right. Rotation toward the buttstock (clockwise) moves the aperture left, which moves the strike of the rounds left.

c.   10-Meter Zero, Setting of the Sights (Mechanical Zero). The gunner indexes or places the elevation knob on a range of 700 meters. He centers the rear peep sight by rotating it clockwise (right) as far as it will go, then rotating counterclockwise (left) five clicks or half-turns. He rotates the windage knob toward the muzzle until the peep sight is completely to the right, then rotates the windage knob toward the buttstock twelve clicks to the left. This places the peep sight in the approximate center of the sight. Each sight may vary as to how many clicks are needed. To check the sight, the gunner starts with the sight all the way to the right and, while counting the clicks, rotates the windage knob until it stops on the left side. He divides the clicks by two. If the click is an uneven number, he rounds it up. To center the sight, he rotates the windage knob toward the center (right) while counting the appropriate number of clicks. He adjusts the sliding scale at the rear of the sight to center the large index line under the zeroed windage mark on the sight. Two threads should be showing on the front sight post. If more or less are showing, the gunner turns in the weapon for maintenance.

Table 1-3. Windage and elevation (peep sight) correction chart.

Table 1-3.   Windage and elevation (peep sight) correction chart.

NOTE:

The primary and spare barrels are zeroed by making adjustments on the front sight.

1-18.   M122 TRIPOD

The M122 tripod provides a stable mount for the M249, and it permits a higher degree of accuracy and control. The tripod is recommended for all marksmanship training and defensive employment.

a.   Mounting the M122 Tripod. The tripod assembly provides a stable and relatively lightweight base that is far superior to the bipod. The tripod may be extended and collapsed without difficulty. It consists of a tripod head, one front leg and two rear legs, and traversing bar. The traversing bar connects the two rear legs. The traversing bar is hinged on one side with a sleeve and sleeve latch on the other. This procedure allows the tripod to collapse to a closed position for carrying or storage, or to lock in an open, extended position for use. The traversing bar also supports the T&E mechanism. Engraved on the bar is a scale, which measures direction in mils. It is graduated in 5-mil increments. It is numbered every 100 mils to 425 mils right of center, and it is numbered every 100 mils to 450 mils left of center.

(1)   The T&E mechanism provides controlled manipulation and the ability to engage predetermined targets.

(a)   The traversing portion of the mechanism consists of the traversing handwheel and traversing slide-lock lever. As the traversing handwheel is turned, the muzzle of the weapon will turn to the left or right, depending on the direction it is turned. Each click of the traversing handwheel indicates a 1 mil change in direction of the muzzle: 1 click equals 1 mil. There is a total of 100 mils traverse (50 mils right and 50 mils left of center).

(b)   The elevating portion of the mechanism consists only of the elevating handwheel. The elevating handwheel has a mil-click device built into it (1 click equals 1 mil). Engraved into the handwheel is a scale divided into 5-mil divisions and 1-mil subdivisions, for a total of 50 mils increments. There are 200 mils above and 200 mils below the zero mark ,for a total of 400 mils in elevation change. Elevation readings are taken in two parts. First, the major reading is taken from the elevation screw plate. The second, minor reading is from the handwheel. The two readings are separated by a slash ("/") when they are recorded.

(c)   The traversing slide-lock lever allows rapid lateral adjustments along the traversing bar. Direction readings are taken from the scale on the traversing bar, using the left side of the traversing slide as an index. The direction of the reading comes from the position of the muzzle, not the position of the slide.

(2)   To set up the tripod, unfold the front leg and spread the rear legs until the leg lock engages. Insert the pintle assembly and rotate the pintle lock-release cam to lock. Ensure that the locking lever of the pintle is facing forward toward the front leg (Figure 1-34).

(3)   Attach the traversing and elevating mechanism (which requires a special adapter). Ensure that the adapter pin is to the right and the opening between it is to the rear. Center the elevating and traversing handwheels. To do this, he rotates the elevation handwheel until about 1-1/2 inches (two fingers) are visible on the upper elevating screw; he rotates the traversing slide until about two fingers are visible on the lower elevating screw. He rotates the traversing handwheel towards his body as far as it will go, then turns it away two complete revolutions. He checks the traversing handwheel scale to ensure the "0" on the scale is aligned with the "0" index line before and after the two revolutions. The T&E is now roughly centered. At night, he positions the traversing mechanism by turning the traversing handwheel toward his body as far as it will go, and then turning it away 50 clicks (two revolutions) (Figure 1-34).

(4)   With the T&E roughly centered, he lowers the traversing slide on to the traversing bar with the locking lever to the rear, and the traversing handwheel to the left, and secures it by turning the locking lever clockwise (Figure 1-34).

(5)   The weapon attaches to the M122 tripod. First, he extends the bipod legs forward. Then, he engages the mounting pins (Located between the front of the handguard and the bipod legs) of the M249 into the pintle of the tripod by squeezing the locking lever of the pintle. He lowers the rear of the weapon so that the hole above the trigger guard can be engaged with the locking pin of the T&E adapter. He aligns the hole with the pin of the adapter and pushes the pin from right to left to secure the M249 to the M122 tripod (Figure 1-34).

(6)   After the M249 is attached and secured to the tripod, the gunner must attach a special ammunition adapter to the M249. He inserts the adapter into the magazine well, as if inserting a magazine. This procedure allows the gunner to use the 200-round drum of ammunition (Figure 1-34).

Figure 1-34. Tripod mount.

Figure 1-34.   Tripod mount.

b.   Dismounting The M249 From The M122 Tripod. The gunner dismounts the M249 from the tripod by first removing the traversing and elevation mechanism from the weapon. He pulls the locking pin of the adapter to release the T&E from the trigger guard. He grasps the carrying handle with his left hand and squeezes the pintle-locking lever with his right hand. He lifts the weapon from the pintle assembly and the tripod.

1-19.   BIPOD OPERATIONS

The bipod group is used to fire from the prone position. The shoulder rest on the buttstock provides support for the gunner when fired in the bipod mode. The gas cylinder group holds the bipod group in place. Once the gas cylinder is removed, the bipod group can also be removed from the receiver.

a.   To lower the bipod legs, hold the legs together and pull down and away from the handguard. Release the legs so that they lock in the vertical position. To extend the bipod legs, grasp the foot of each leg and pull down (Figure 1-35).

Figure 1-35. Lowering of the bipod.

Figure 1-35.   Lowering of the bipod.

b.   To retract the bipod legs, push in the latches and push in the legs.

c.   Before transporting the weapon, the gunner folds the bipod legs. To place the legs in the closed position, the gunner holds them together; he pulls the them back under the handguard; he then releases them so that the hooks on the legs grip the handguard. The bipod can be folded only when the legs are in the closed position (Figure 1-36).

Figure 1-36. Folding of bipod under the handguard.

Figure 1-36.   Folding of bipod under the handguard.

1-20.   VEHICULAR MOUNT

The standard vehicular mount for the M249 machine gun is the M6 pedestal mount used on the (HMMWV). One component of the pedestal mount is the M197 machine gun mount (travel lock). This mount also adapts to other vehicles (Figure 1-37).

a.   To mount the weapon, the gunner ensures that the release lever of the pintle is facing forward. To extend the bipod legs forward, he places the front mounting pins of the M249 into the pedestal by squeezing the locking lever of the pintle. He ensures that the M60 machine gun adapter assembly is pivoted away from the M249 fork (clevis). He lowers the rear of the weapon so that the locking pin of the machine gun mount can engage the hole above the trigger guard. The gunner engages this part of the weapon into the fork of the mount and pushes in the locking pin.

b.   To dismount the weapon, the gunner pulls the locking pin of the mount. He raises the rear of the weapon slightly and squeezes the locking lever of the pintle. Once the front mounting pins are released, the gunner lifts the weapon from the mount.

Figure 1-37. Vehicular mount.

Figure 1-37.   Vehicular mount.

1-21.   TRIPOD POSITIONING

The M122 tripod provides a stable mount for the M249, and it permits a high degree of accuracy and control. The gunner unfolds the front leg and positions it toward the target and spreads the rear legs until the leg lock engages.

Section IV. PERFORMANCE PROBLEMS AND DESTRUCTION

This section identifies some of the problems that cause the M249 to perform improperly. It also explains how to identify unserviceable parts and how to destroy the M249 when authorized to do so.

1-22.   MALFUNCTIONS

A malfunction occurs when a mechanical failure causes the M249 to fire improperly. Defective ammunition or improper operation by the automatic rifleman is not considered a malfunction. If cleaning and or lubricating the weapon does not fix the problem, then it is turned in to the unit armorer. Table 1-4 shows malfunctions, their probable causes, and the corrective actions.

MALFUNCTION

PROBABLE CAUSES

CORRECTIVE ACTIONS

Sluggish operation.

Lack of lubricant.

Carbon buildup in the gas system.

Burred parts.

Lubricate.

Clean the gas regulator, piston, and cylinder.

Notify unit maintenance.

Failure to cock or a runaway weapon.

Broken, worn, or burred sear.

Piston assembly sear notch worn.

Sear stuck in trigger housing.

Short recoil.

Carbon buildup in the gas system.

Notify unit maintenance.

Notify unit maintenance.

Notify unit maintenance.

Clean and lubricate the bolt and slide assembly.

Clean the gas regulator, piston, and cylinder.

Table 1-4.   Malfunctions.

1-23.   STOPPAGES

A stoppage is any interruption in the cycle of functioning caused by faulty action of the weapon or faulty ammunition.

a.   Stoppages are classified by their relationship to the cycle of functioning. Table 1-5 shows types of interruptions or stoppages, their probable causes, and the corrective actions.

Table 1-5. Stoppages.

Table 1-5.   Stoppages.

DANGER

IF NOTHING IS EJECTED AND THE WEAPON IS HOT (200 OR MORE ROUNDS FIRED IN LESS THAN 2 MINUTES), DO NOT OPEN THE COVER. PUSH THE SAFETY TO THE RIGHT (RED RING NOT VISIBLE), WHICH PLACES THE WEAPON ON SAFE. KEEP THE WEAPON POINTED DOWNRANGE FOR 15 MINUTES, THEN CLEAR THE WEAPON. BE CAREFUL CLEARING THE WEAPON WHEN THE BARREL IS HOT; A ROUND MAY FIRE (COOK OFF) DUE TO THE BARREL'S HEAT INSTEAD OF THE FIRING MECHANISM. DURING TRAINING OR ON A FIRING RANGE, AFTER THE WEAPON HAS FIRED 200 ROUNDS, THE BARREL IS CONSIDERED "HOT."

  • DURING COMBAT, WAIT 5 SECONDS (BECAUSE OF THE POSSIBILITY OF A HANGFIRE) BEFORE APPLYING IMMEDIATE ACTION OR REMEDIAL ACTION.
  • DURING TRAINING, WAIT 15 MINUTES BEFORE CLEARING A HOT WEAPON AND APPLYING IMMEDIATE OR REMEDIAL ACTION.

b.   If a round is in the chamber (this means any part of the round, ranging from the tip of the bullet to the rim) when applying immediate or remedial action on a cold or hot gun. The gunner removes the ammunition from the feed tray only, then closes the cover and attempts to fire. If the weapon fires, he reloads and continues firing. If it does not fire, he clears the weapon (removes the round using a clearing rod, with the cover closed). He does not use anything other than a cleaning rod. Then, he inspects weapon and ammunition.

1-24.   IMMEDIATE ACTION

Immediate action is action taken to reduce a stoppage without looking for the cause. Immediate action should be taken in the event of a misfire or a cook off. A misfire is the failure of a chambered round to fire. Such failure can be due to an ammunition defect or faulty firing mechanism. A cook off is the firing of a round due to the heat of a hot barrel and not to the firing mechanism. Cook offs can be avoided by applying immediate action within 10 seconds of a failure to fire. The gunner keeps the M249 on his shoulder while performing immediate action procedures. If the M249 stops firing, he takes the following immediate actions. An effective memory aid is POPP, which stands for Pull, Observe, Push, and Press:

a.   Pull and lock the cocking handle to the rear while observing the ejection port to see if a cartridge case, belt link, or round is ejected. Ensure that the bolt remains to the rear to prevent double feeding if a round or cartridge case is not ejected.

b.   If a cartridge case, belt link, or round is ejected, push the cocking handle to its forward position, take aim on the target, and press the trigger. If the weapon does not fire, take remedial action. If a cartridge case, belt link, or round is not ejected, take remedial action.

1-25.   REMEDIAL ACTION

Remedial action is any action taken to determine the cause of a stoppage and to restore the weapon to an operational condition. This action is taken only after immediate action does not remedy the problem.

a.   Cold Weapon Procedures. When a stoppage occurs with a cold weapon, and if immediate action has failed, use the following procedures:

(1)   While the weapon is on your shoulder, grasp the cocking handle with the right hand, palm up; pull the cocking handle to the rear, locking the bolt. While holding the resistance on the cocking handle, move the safety to SAFE and return the cocking handle.

(2)   Place the weapon on the ground or away from your face. Open the feed cover and perform the five-point safety check. Reload and continue to fire.

(3)   If the weapon does not fire, clear the weapon and inspect it and the ammunition.

b.   Hot Weapon Procedures. If the stoppage occurs with a hot weapon (200 or more rounds in less than 2 minutes, or as noted previously for training), move the safety to SAFE, wait 5 seconds (during training, let the weapon cool for 15 minutes), and use the same procedures as outlined for cold weapon procedures.

c.   Jammed Cocking Handle. If a stoppage occurs, and if the cocking handle cannot be pulled to the rear by hand (the bolt may be fully forward and locked or only partially forward), the gunner takes the following steps:

(1)   Tries once again to pull the cocking handle by hand.

CAUTION
Do not try to force the cocking handle to the rear with your foot or a heavy object. This could damage the weapon.

(2)   If the weapon is hot enough to cause a cook off, moves all Soldiers a safe distance from the weapon and keeps them away for 15 minutes.

(3)   After the gun has cooled, opens the cover and disassembles the gun. Ensures rearward pressure is kept on the cocking handle until the buffer is removed. (The assistant gunner helps the gunner do this.)

(4)   Removes the round or fired cartridge. Uses cleaning rod or ruptured cartridge extractor if necessary.

(a)   In a training situation, after completing the remedial action procedures does not fire the gun until an ordnance specialist has conducted an inspection.

(b)   In a combat situation, after the stoppage has been corrected, the gunner changes the barrel and tries to fire. If the weapon fails to function properly, he sends it to the unit armorer.

1-26.   DESTRUCTION PROCEDURES

Destruction of any military weapon is only authorized as a last resort to prevent enemy capture or use. This paragraph discusses the field-expedient means of this destruction; it does not replace published policies. In combat situations, the commander has the authority to destroy weapons, but he must report this destruction through channels.

a.   Disassemble the weapon as completely as time permits. Use the barrel to destroy the bolt, operating rod group, bipod, sights (rear and front), and receiver.

b.   Bury the disassembled weapon or dump the parts into a stream, a sump, or a latrine.

c.   Burn the weapon by placing an incendiary grenade on the receiver group over the bolt (with the cover feed mechanism assembly resting on the grenade) and detonating the grenade.



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