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M240B Gunners Training


M240B Gunners TrainingM240B
General Overview of the Basics Of the M240B Machine Gun
Characteristics and Capabilities of the M240B Machine Gun.
Malfunctions and Stoppages
Immediate/Remedial action
Characteristics of fire
Classes of Fire
Cycles of Functioning
Fire Control/Fire Commands
Range Card




Characteristics and Capabilities of the M240B Machine Gun
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Purpose of development-
Because of the reliability and maintainability concerns with the M60 machine gun, the United States Army initiated a new machine gun upgrade. Following rigorous technical and operational testing of the upgraded M60-series and the M240-series machine guns, the M240B machine gun is now selected to fill the Army's needs for a new machine gun.

Role of the M240B machine gun-
The M240B machine gun supports ground forces in both offensive and defensive operations. Designed as a tripod mounted or bipod mounted supported machine gun that provides the heavy volume of close and continuous fire that a soldier needs to accomplish his mission.

General data of the M240B machine gun-
The M240B is a general-purpose machine gun. It is capable of sustained high volumes of fire for prolonged periods without adverse effects on the weapon. The machine gun is designed as a tripod mounted or bipod supported machine gun for use by ground forces. The bipod is integrated into the receiver assembly of the weapon. The M240B is gas operated, mounted on a coaxial mount, and fires from the open bolt position. The 7.62-mm is the authorized ammunition for this machine gun, ammunition is fed by a metallic split-link belt. The M240B has a buttstock and can be ground mounted on a M122A1 tripod mount or integral bipod. Safety is ensured by positive locking of the breechblock before the round is fired; the round cannot be struck before locking is completed. The M240B fires from the open breech. The working parts are protected by the body of the weapon. The gas from firing one round provides the energy for firing the next round. Thus, the gun functions automatically as long as it is supplied with ammunition and the trigger is held to the rear. As the gun is fired, the belt links separate and are ejected from the side. Empty cases are ejected from the bottom of the gun. A spare barrel is issued with each M240B, and barrels can quickly be changed as the gun has a fixed head space. However, barrels from different guns should not be interchanged. The bores of the barrels are chromium plated, reducing barrel wear to a minimum. The feed tray cover allows for the cover to be closed with the bolt in the forward or rear position without damage.


Ammunition
7.62-mm ball, tracer, armor-piercing, armor- piercing-incendiary, blank, dummy. Armor-piercing and armor-piercing-incendiary are not authorized for training.

Weight of the M240B
Approximately 27.6 pounds

Weight of barrel
Approximately 6.6 pounds

Weight of M122 tripod w/pintle and flex-mount
Approximately 20 pounds

Overall Length
Approximately 49 inches

Rifling
4 grooves with a uniform right-hand twist, 1 turn in 12 inches

Muzzle velocity
2800 feet/second

Limits of Traverse     (M122 tripod)
With T & E mechanism                      100 mils
Using traversing bar                             875 mils
Free gun                                              6400 mils

Limits of elevation and depression (M122 tripod)
With T & E mechanism                      + or - 200 mils
Free gun                                              + or - 445 mils

Rates of fire

Sustained- 100 Rounds per minute, barrel change every 10 minutes, 4-5 seconds between bursts
           
Rapid- 200 Rounds per minute, barrel change every 2 minutes, 2-3 seconds between bursts

Cyclic- 650-950 Rounds per minute, barrel change every minute


Range

Maximum-                               3725 meters

Maximum effective-                1100 meters w/ Tripod and T&E

Area
Tripod-                                    1100 meters
Bipod-                                     800 meters

Point
Tripod-                                    800 meters
Bipod-                                     600 meters

Suppression                             1800 meters

Grazing fire                             600 meters

Tracer Burn out                       900 meters


Malfunctions and Stoppages
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Malfunction

Malfunction: A malfunctioning machine gun is a gun that is not firing properly

The two types of malfunctions are; Sluggish Operation and Uncontrolled fire (Runaway gun)

Sluggish Operation: Sluggish operation usually is due to excessive friction caused by carbon, lack of proper lubrication, burred parts, or excessive loss of gas.

Uncontrolled fire: Uncontrolled fire is usually caused by the gunner not pulling and holding the trigger all the way to the rear. This results in the sear not clearing the sear notch, which causes wear to both parts.

Stoppages

Stoppages: A stoppage is any interruption in the cycle of functioning caused by faulty action of the gun or faulty ammunition. Stoppages are classified by their relationship to the Cycle of functioning.

There are 6 types of stoppages:

            Failure to feed- Rounds are not pulled into the feed-tray and aligned

Failure to chamber- Round is not de-linked and pushed into the chamber

            Failure to lock- Bolt fails to lock inside the chamber

            Failure to fire- Round fails to fire

            Failure to extract- Round is not pulled from the chamber

            Failure to cock- Operating rod fails to cock the sear.


Immediate/Remedial action
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Immediate action

Immediate action- Immediate action is action taken to reduce a malfunction or stoppage without looking for the cause.

Misfire- A misfire is the failure of a chambered round to fire. A misfire is not dangerous, but it is handled as described below.

Cookoff- A cookoff is the firing of a round by the heat of a very hot barrel, and not by the firing mechanism. A cookoff can be avoided by applying immediate action within 10 seconds after a failure to fire.

  • Cock the gun, and watch the ejection port to see if a cartridge case, belt link, or round is ejected. Insure that the bolt remains to the rear to prevent double feeding if a round or cartridge case is not ejected.

  • If a cartridge case, belt link, or round is ejected, return the cocking handle to the forward position, re-lay on the target, and attempt to fire. If the gun still does not fire, clear it and inspect the ammunition and the gun to determine the cause of the stoppage.

  • If a cartridge case, belt link, or round is not ejected, take remedial action

Remedial Action

Remedial action- Remedial action is the action taken to reduce a stoppage with an attempt to determine cause.

Remedial action is taken differently depending on whether the gun is a "hot gun" or "cold gun".

Cold gun-
If the stoppage occurs with a cold gun, raise the feed-tray cover and remove the belt of ammunition. Raise the feed-tray and inspect the chamber.

If there is no round in the chamber, reload and attempt to fire. If the gun fires, continue firing. If it does not fire, reapply immediate and then remedial action as necessary. Inspect the round and chamber.

If there is a round in the chamber, close the feed-tray cover and attempt to fire. If the gun fires, reload and continue firing. If it does not fire, clear the gun and inspect the gun and ammunition.

Hot gun- (more than 200 rounds fired in two minutes)
If the stoppage occurs with a hot gun, Move the safety to safe, raise the feed-tray cover, and remove the ammunition belt. Raise the feed-tray and inspect the chamber.

Note- During training, an experienced gunner should wait 15 minutes and the clear the gun.

If there is no round in the chamber, reload and try to fire. If the gun fires, continue firing. If it does not fire, reapply immediate action immediate and remedial action as necessary. Inspect the gun and ammunition.

If there is a round in the chamber, close the feed-tray cover and attempt to fire. If the gun fires, reload and continue firing. If it does not fire during combat, change barrels, reload and continue firing. If the gun does not fire during training, wait 15 minutes and then clear the gun and inspect it for a cause.

Characteristics of fire
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Characteristics of fire are defined as Trajectory, Maximum Ordinate, Cone of Fire, Beaten Zone, and Danger space. A gunner must learn and understand each one of these in order to deliver the most effective and devastating fire from there machine gun.

Trajectory- This is the path of a bullet during flight. It is almost flat at range of 300 meters or less. At ranges beyond 300 meters, the trajectory is curved, and the curve becomes greater as the range increases.

Maximum Ordinate- This is the highest point the trajectory reaches between the muzzle of the gun and the base of the target. It always occurs at a point approximately two-thirds of the distance from the gun two the target. The maximum ordinate increases as the range increases.

Cone of Fire- This is the pattern formed by the different trajectories in each burst as they travel down range. When several rounds are fired in a burst from the machine gun, each round takes a slightly different trajectory. This is primarily caused by the vibration of the gun. Variations in ammunition and atmospheric conditions also contribute to the different trajectories.

Beaten Zone- This is the pattern formed by the rounds within the cone of fire striking the ground or target. The size and shape of the beaten zone changes when the range to the target changes or when the machine gun is fired into different types of terrain. On uniformly sloping or level terrain, the beaten zone is long and narrow. As the range to the target increases, the beaten zone becomes shorter and wider. When fire is delivered into terrain sloping down and away from the gun, the beaten zone becomes longer. When fire is delivered in to rising terrain, the beaten zone becomes shorter. The terrain has no great effect on the width of the beaten zone.

Danger Space- This is the space between the gun and the target where the trajectory does not rise more than 1.8 meters. This includes the area of the beaten zone.
When a machine gun is fired over level or uniformly sloping terrain at a target less than 700 meters away, the trajectory will not rise above the height an average man.
When engaging targets over level or uniformly sloping terrain at ranges greater than 700 meters, the trajectory will rise above the average height of a soldier. Therefor, not all the distance between the gun and the target is danger space.

Classes of Fire
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Machine gun fire is classified with respect to the GROUND, the TARGET, and the GUN.

Fire with respect to the GROUND includes:

Grazing Fire- When the center of the cone of fire does not rise more than 1 meter above the ground. When firing over level or uniformly sloping terrain, a maximum of 600 meters of grazing fire can be obtained.

Plunging Fire- When danger space is practically confined to the beaten zone. Plunging Fire occurs when firing at long ranges, when firing from high ground to low ground, when firing into abruptly rising ground, or when firing over across uneven terrain, resulting in a loss of grazing fire at any point along the terrain.

Fire with respect to the target includes:

Frontal Fire- When the long axis of the beaten zone is at a right angle to the front of the target. Simply stated, that means when firing directly into the front of a target.

Flanking Fire- When delivered directly against the flank of a target.

Oblique Fire- When the long axis of the beaten zone is at an angle other than a right angle to the front of the target.

Enfilade fire- When the long axis of the beaten zone coincides or nearly coincides with the long axis of the target. This type of fire is either frontal or flanking. It is the most desirable type of fir with respect to a target because it makes maximum use of the beaten zone.


Fire with respect to the gun includes:

Fixed Fire- that delivered against a stationary point target when the depth and the width of the beaten zone will cover the target.

Traversing Fire- That distributed in width by successive changes in direction.

Searching Fire- That distributed in depth by successive changes in elevation.

Traversing and Searching Fire- That distributed in width and depth by successive changes in direction and elevation.

Swinging Traverse Fire- That delivered against targets too wide to cover with the traversing handwheel.

Free Gun- That delivered from a tripod mounted machine gun against targets requiring rapid major changes in direction and elevation which cannot be applied to the Traversing and Elevating mechanism.

Cycles of Functioning
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Crew members can recognize and correct stoppages when they know how the gun functions. The gun functions automatically as long as ammunition is fed into it and the trigger is held to the rear. Each time a round fires, the parts of the gun function in sequence. Many of the actions occur at the same time and are separated only for teaching purposes. The sequence of functioning is known as the "CYCLE OF FUNCTIONING". As a minimum standard, the soldier should know the eight basic terms and short definitions of each.

    1. Feeding- A round is positioned in the feed-tray groove.

    1. Chambering- A round is stripped from the belt and placed into the chamber.

    1. Locking- The bolt is locked inside the barrel socket.

    1. Firing- The firing pin strikes and fires the primer, which fires the cartridge.

    1. Unlocking- The bolt is unlocked from the barrel socket.

    1. Extracting- The empty cartridge case is pulled form the chamber.

    1. Ejecting- The empty cartridge case is thrown from the receiver.

    1. Cocking- The sear engages the sear notch on the operating rod.

Fire Control/Fire Commands
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Methods of fire control:

The noise and confusion of battle may limit the use of some of these methods; therefore, the leader must select a method or combination of methods that will best accomplish the mission.

Oral. This is an effective method of control, but at times the leader may be too far away from the crews, or the noise of battle may make it impossible for the crews to hear him.

Arm-and Hand Signals. These are either visual or sound signals such as pyrotechnics or blasts on a whistle. These signals should be included in standing operating procedures and must be understood by all squad members.

Personal Contact. In many situations, the leader must move to individual crewmembers to issue orders. This method of control is used more than any other by small-unit leaders. The leader must use maximum cover and concealment to keep from disclosing the position.

Standing Operating Procedures. SOPs are actions to be executed without command. SOPs are developed during the training of the gun crews. Their use eliminates many commands and simplifies the leader's job of fire control.

Fire Commands:

A fire command is given to deliver effective fire on a target quickly and without confusion. When the leader decides to engage a target that is not obvious to the gunners, he must provide them with the information they need to effectively engage the target. He must alert the crews, and give a target direction, description, and range; the method of fire; and the command to fire.

There are initial fire commands and subsequent fire commands. Initial fire commands are given to begin firing at a target, and subsequent fire commands are given to adjust direction and elevation, change the rate of fire after a fire mission is in progress, interrupt fire, or terminate the alert.

Elements of Fire Commands. Fire commands for all direct fire weapons follow a pattern that includes similar elements. There are six elements in the fire command for the machinegun: ALERT, DIRECTION, DESCRIPTION, RANGE, METHOD OF FIRE, and COMMAND TO OPEN FIRE. The crew repeats each element of a fire command as it is given.

Range Card
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A Range Card is a record of the firing data required to engage predetermined targets during limited visibility. There are two types of range cards applicable to the M240B Machinegun, one has a FPL and the other has a PDF. Predetermined targets can include likely avenues of approach; likely sites for enemy crew served weapon positions, and likely enemy avenues of approach, as well as a PDF or FPL and other target areas. The range card may also be used as a reference to engage targets when visibility is good. It aids the Platoon Leader in preparing his defense plan.

The Tripod mounted machine gun is normally used to cover the primary sector of fire. Predetermined targets in the secondary sector are engaged from the bipod mode.

A range card has two parts, a sketch and a data section. The sketch section is not drawn to scale but the data section must be accurate.

Range Cards are prepared in duplicate, one copy stays at the position and the other is forwarded to the PL. Complete range cards are prepared for the primary position and partial range cards for the alternate and supplementary positions. Range cards are prepared immediate upon arrival in a position, regardless of the anticipated stay. Range cards will be continually updated through out the occupation of the position.

Range card preparation:

In preparing a range card there is no set sequence in filling out the range card except for step 1 (position the gun and tripod).

  1. Position the gun;
Mount the machine gun on the tripod.
Position the gun with the muzzle pointing in the direction of the FPL (metal to metal left or right) if a FPL is not assigned point the gun in the PDF (should be centered but not always).
  1. Fill in marginal data;
Fill in Platoon and company info (Squad in used for mechanized units)
Fill in position ID (i.e. Primary, alternate or supplementary) it is also a good idea to place the clock position.
Fill in the date time Group (day, time, month, year)
Fill in weapon data (Weapon type and admin number i.e. Gun 5)
  1. Fill in magnetic north;
Orient the range card and place the north-seeking arrow in the direction of magnetic north,


  1. Draw in your primary and secondary sectors of fire;
Sketch the basic machine gun symbol if using a FPL extend the basic symbol in the direction of the FPL. If a PDF is assigned, draw a machine gun symbol in the direction of the PDF.
When using a FPL include grazing fire (shaded blade) make sure to include sections that cannot be covered by grazing fire. This is shown by breaks in the shaded area, label these brakes in meters at the beginning and ending of the break. Label the top of the FPL with the degrees.
Draw in the opposite primary sector limit. No data need be recorded in the data section unless a target is located along this line. When a FPL is assigned, it is always labeled target 1. If the opposite side of the traversing bar cannot be used to mark the opposite side of the primary sector, a direction must be recorded in the sketch section.
Draw in the limits of the secondary sector of fire with broken lines.
  1. Fill in the each circle represents;
Determining the value of each circle by finding a terrain feature or target farthest from the position that is within the weapons capability. Determine the range to the object and round to the nearest 100 meters. Sketch the object on the appropriate circle in relation to the gun on the range card. Find the maximum number of circles that will divide evenly, the result is the value of each circle. Enter that value on the range card.
  1. Draw in your sector sketch
Sketch all targets in both your primary and secondary sector of fire. Include dead space.
  1. Enter your target data
Targets in the primary sector are shown on the range card sketch by numbers enclosed in circles. A FPL, when assigned is always labeled as target number 1. Other targets are assigned subsequent numbers in the order of their tactical importance.
Wide targets in the primary sector are usually engaged in the center first. However, the initial burst can be positioned wherever the leader desires. The gunner first measures the entire target width. He writes the width in the data section as TW-20. He then lays on the point on the target where the initial burst is desired and traverses to one edge of the target while counting the clicks. The number of clicks he traverses and the direction he moves the barrel must also be recorded in the data section--for example, TW-20/R7, this would tell the gunner that he was not laid on the center of the target initially. Furthermore, after the initial burst, he must traverse right 7 clicks to reach the right edge of his target and then back 20 clicks to cover the entire target area. If the gunner were laid on the left edge of his target, his remark in the data section would be TW-20/R20.
  1. Orient the gun with a prominent terrain feature;
Obtain a magnetic azimuth to or from the terrain feature (recognizable on a map) to the tripod mounted machine gun position. Draw a line between these two points. Place arrow barbs along this line in the direction the magnetic azimuth was taken. Record the distance in meters above the barbed line; record the magnetic azimuth in mils or degrees below the barbed line. If a prominent terrain feature is not available, the gun position will be identified by an eight-digit grid coordinate.




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