M2 Class Machine Gun – The “Ma Deuce” .50BMG

United States Marine Corps

Weapon Systems Series


RoleThe M2HB .50-caliber machinegun supports the infantryman in both the offense and the defense by providing a heavy volume of accurate, long-range fire.

Five Capabilities The five capabilities of the M2HB .50-caliber machinegun are to:

  • Support the infantryman in the offense and the defense
  • Provide a heavy volume of close, accurate, and continuous fire when in an attack
  • Provide long range, close defensive, and final protective fires as part of a unit’s defensive lines
  • Provide reconnaissance by fire on suspected enemy positions
  • Protect motorized movements
  • Defend against low-flying, hostile aircraft
  • Destroy lightly armored vehicles

M2HB .50 The operator must understand the characteristics of the .50-caliber caliber machinegun to have success on the battlefield The picture below shows the Machinegun

Browning M2HB .50-caliber machinegun on an M3 tripod mount.

Major Components The M2HB .50-caliber machinegun can be broken down into eight major components pictured below.

Weight The following table lists the weight of the major parts of the M2HB .50caliber machinegun.

Component Part Weight (in pounds)
Receiver group 60
Barrel Approximately 24
M3 tripod mount 44
Total weight Approximately 128

Length The following table lists the length of the M2HB .50-caliber machinegun.

Item Length (in inches)
Length of barrel 45
Length of gun, overall Approximately 65

Range The following table lists the range of the M2HB .50-caliber machinegun.

Type of Range Range (in meters)
Maximum 6,767
Maximum Effective 1,830
Grazing fire 700

Rates of Fire The following table lists the rates of fire of the M2HB .50-caliber machinegun.

Type of Fire Rate (rounds per minute)
Sustained Less the 40
Rapid More than 40
Cyclic 400-550

Muzzle Velocity The muzzle velocity of the M2HB .50-caliber machinegun is 3,050 feet per second.

Descriptive Characteristics The M2HB .50-caliber machinegun is

  • Belt-fed. By repositioning some of its component parts, the gun is capable of alternate feed (ammunition can be fed from either the right or left sides). The infantry generally uses left side feed. A disintegrating metallic link belt is used for feeding.
  • Air-cooled. The maximum surface of the barrel and receiver is exposed to permit air-cooling. Perforations in the barrel support allow air to circulate around the breech end of the barrel and help in cooling the parts. The heavy barrel is used to delay early overheating.
  • Recoil-operated. The expanding powder gases (which various springs, cams, and levers control) provide the force for recoil operation.

Purpose You must mount the M2HB .50-caliber machinegun to fire. Along with the mount, you need to install a traversing and elevating mechanism to permit a high degree of accuracy and control.

M3 Tripod The M3 tripod mount is the principal ground mount for the M2HB .50Mount caliber machinegun shown in the picture below.

The tripod has three folding, telescopic legs that can be stomped into the ground for greater stability. The gun is connected to the tripod by a pintle that is semi-permanently attached to the gun. The pintle seats into the tripod head and is locked in place.

A traversing bar between the two trail legs serves as a support for the traversing and elevating (T&E) mechanism. The T&E mechanism attaches to the rear of the gun and is locked onto the traversing bar.

The M2HB .50-caliber machinegun can be mounted on two different mounts: Pintle Vehicle Mount and the High mobility multipurpose wheeled vehicle (HMMWV) weapons station M66 ring mount. Each of these mounts has a pintle adapter that accepts the pintle shown below.

HMMWV Weapons StationThe HMMWV weapons station has a ring mount that, used with the MK64 cradle mount, will accept the M2HB .50-caliber machinegun, as pictured below.

M66 Ring The M66 ring mount is installed on trucks and other combat vehicles. A Mount truck mounted version is shown below.

T&E Mechanism

Used on both ground and vehicle mounts, the T&E mechanism for the M2HB .50-caliber machinegun

  • Secures the rear of the machinegun to its mount.
  • Permits fire control adjustment.
  • Allows the machinegun to traverse 400 mils to the left or right of the 0 index on the traversing bar on the M3 tripod mount.
  • Allows the elevation of the machinegun to range from 100 mils in elevation to 250 mils in depression. Note: For more information on the T&E mechanism, see study unit 7.

AN/TVS-5 Night Vision Sight The AN/TVS-5 night vision sight, used for passive night observation and fire, can be mounted on the M2HB .50-caliber machinegun. Portable and battery operated, the AN/TVS-5 night vision sight amplifies natural light such as moonlight, starlight, and skyglow without emitting visible or infrared light that the enemy can detect.

Ammunition The M2HB .50-caliber machinegun cartridge consists of a cartridge case, Types primer, propelling charge, and bullet. The table below describes the types of ammunition, each identifiable by the color of the tip.

Type Color of tip Used for
Ball (M2, M33) No color Marksmanship training Anti-personnel Light material targets
Tracer (M1, M10, M17) Red, maroon, or orange Aiding in observing fire Incendiary effect Signaling
Armor-piercing (M2) Black Armored aircraft Lightly armored vehicles Concrete shelters Other bullet-resisting targets
Incendiary (M1, M23) Blue or light blue Incendiary effect, especially against aircraft
Armor-piercing incendiary (M8) Aluminum-colored Combined armor-piercing and incendiary effect
Armor-piercing incendiary tracer (M20) Aluminum with red tip Combined armor-piercing and incendiary effect Additional tracer features
Blank (M1, M1A1) No bullet Simulated firing
Dummy (M2) No color on tip; holes in cartridge case Instructional purposes (completely inert)
Sabot light armor penetrator (SLAP) M903 Plastic sleeve on projectile Armor piercing

Eight Steps The cycle of operation of the M2HB .50-caliber machinegun consists of the following eight steps:

1 Firing. The firing pin is released, igniting the primer of the cartridge.
2 Unlocking. The bolt is unlocked from the barrel and barrel extension.
3 Extracting. The empty cartridge case is pulled from the chamber.
4 Ejecting. The empty cartridge case is expelled from the receiver.
5 Cocking. The firing pin is withdrawn into the cocked position.
6 Feeding. During feeding, the cartridge is placed in the receiver.
7 Chambering. During chambering, the cartridge is placed into the chamber of the weapon.
8 Locking. The bolt is locked to the barrel and barrel extension.

Procedures Before you begin disassembly of the M2HB .50-caliber machinegun, you must clear it to make sure it is completely safe. The steps to clear the weapon are listed in the table below.

1 Place the gun in the single shot mode by rotating the buffer tube sleeve to the right and releasing the bolt latch to the up position as shown in the picture below.
2 Raise the feed cover by rotating the cover latch forward and lifting straight up as shown in the picture below.
3 Remove ammunition if present.
4 Close the feed cover assembly.
5 Grasp the slide handle and lock the bolt to the rear.
6 Open the feed cover assembly.
7 Inspect the T slot on the face of the bolt and chamber.
8 Press the bolt latch release and ride the bolt forward.
9 Close the feed cover assembly. Note: Never close the cover with the bolt to the rear.

Procedures After you clear the M2HB .50-caliber machinegun, you may begin disassembly into the six main groups for cleaning and inspection. Disassembly consists of the following sequential steps:

Action…removing the
1 Barrel group
2 Backplate
3 Drive spring rod assembly
4 Bolt group
5 Barrel extension
6 Barrel buffer body
7 Barrel buffer assembly

Components The picture below shows the components of the M2HB .50-caliber machinegun.

Barrel Group Disassembling the barrel group consists of the steps listed in the table below.

1 Turn the cover latch and raise the cover group as shown below.
2 Pull the retracting handle back until the lug on the barrel locking spring aligns with the 3/8-inch hole on the right side of the receiver.
3 Turn the barrel clockwise until it disengages.
4 Set the barrel aside, being careful not to damage the threaded end.

Backplate To remove the backplate, follow the steps listed in the table below.

1 Pull out on the backplate latch lock and up on the backplate latch as shown in the picture below. Note the placement of the hands in the picture.
2 Lift the entire backplate straight up.
3 Set the backplate aside with the handles down.

Drive Spring The drive spring on the M2HB .50-caliber machinegun is located on the right Rod Assembly side of the receiver as shown in the picture below.

The table below lists the steps to remove the drive spring.

Removing the
Drive Spring

1 Push in on the head of the drive spring and then slightly to the left to unseat it from the right side plate. WARNING: Never attempt to cock the gun while the backplate is off and the drive spring is in place. The drive spring can seriously injure you if it is compressed and slips from its seat in the sideplate.
2 Pull the drive spring to the rear and out of the receiver.

Bolt Group Remove the bolt group from the receiver by following the steps listed in the table below.

1 Grasp the retracting slide handle and give it a quick jerk, freeing the bolt from the barrel extension.
2 Align the collar of the bolt stud with the clearance hole in the bolt slot on the right sideplate and remove the bolt stud as shown below.
3 Slide the bolt to the rear and out of receiver as shown below.
4 Place the bolt down on its right side (with the extractor arm up) so that the extractor will not fall from the bolt.

Barrel The following table lists the steps to remove the barrel buffer body group and Extension and the barrel extension group from the M2HB .50-caliber machinegun. Buffer Body Group

1 Insert a combination tool (or pointed instrument) through the hole in the lower rear corner of the right sideplate.
2 Push in on the barrel buffer body lock. At the same time, place one hand on the receiver and push the barrel extension and barrel buffer body groups to the rear as shown in the picture below.
3 Remove both groups from the receiver.
4 Separate the two groups by pushing forward on the tips of the accelerator as shown below.

Barrel Buffer The last step to disassembly is to pull the barrel buffer assembly from the rear Assembly of the barrel buffer body group as shown below:


Estimated 25 minutes
Study Time
Lesson Scope This lesson discusses how to assemble and perform a function check on the
M2HB .50-caliber machinegun.
Learning After completing this lesson you should be able to
Identify the steps to assemble the M2HB .50-caliber machinegun.
Identify the steps to perform a function check on the M2HB .50-caliber

In This Lesson This lesson contains the following topics:

Topic See Page
Introduction 5-35
Assembling 5-36
Performing a Function Check 5-41
Lesson 3 Exercise 5-49

Procedure To assemble the .50-caliber machinegun, replace the groups in the reverse order of disassembly. Assembly is accomplished by completing the procedures below.

  • Connect the barrel buffer group
  • Install the barrel buffer and extension groups
  • Install the bolt stud
  • Replace the drive spring
  • Replace the backplate
  • Replace the barrel

Connecting the Barrel Buffer Group The following table lists the steps to connect the barrel buffer assembly and the barrel buffer body.

1 Turn the barrel buffer tube until the screwdriver slot in the rear of the tube is vertical and the arrow points to right, as shown below:
2 Push the barrel buffer assembly fully forward, as shown below:

Install the Barrel Buffer and Extension Groups The following table lists the steps to join the barrel buffer and the barrel extension groups.

1 Hold the barrel buffer group in your right hand with your index finger supporting the accelerator.
2 Join the notch on the shank of the barrel extension group with the cross-groove in the piston rod of the barrel buffer assembly. At the same time, align the breech lock depressors with the guideways in the sides of the barrel extension, as shown below.
3 Push the groups together. Note: The accelerator should rotate rearward.
4 Place the groups in the receiver and push them forward until the barrel buffer body spring lock snaps into position. Note: The barrel buffer tube should protrude about 1 1/8 inches from the rear of the barrel buffer body group.

Install Bolt Stud The following table lists the steps to install the bolt stud and lock the barrel buffer, barrel extension group, and the bolt into receiver.

1 Look at the bolt to be sure the extractor assembly is down and the cocking lever is inclined to the front.
2 Align the rails on the bolt with the grooves on the barrel extension and slide bolt about halfway onto the barrel extension.
3 Insert the barrel buffer, barrel extension, and bolt into the back of the receiver as shown below. Note: You should hear two clicks One for the body lock snapping in Another for the bolt latch connecting with the top of the receiver.
4 Press up on the bolt latch and push the bolt forward until the hole is aligned with the clearance hole on the right side of the receiver.
5 Replace the bolt stud and push the bolt as far forward as you can, as shown below.

Replace the Drive Spring The following table lists the steps to replace the drive spring.

1 Insert the spring into its hole in the rear of the bolt and push it all the way in.
2 Press in and to the right until the retaining pin slips into the hole on the right sideplate. Note: The spring will be slightly compressed.
3 If the buffer does not go all the way into the receiver with the bolt, take the barrel buffer, barrel extension, and bolt out of the receiver and repeat the above steps.

Replace the Backplate The following table lists the steps to replace the backplate.

1 Pull the backplate latch lock out and slide the backplate onto the back of the receiver.
2 Continue to hold the backplate latch lock out and lightly tap the backplate down with your hand until it is all the way down as shown in the picture below.
3 Release the latch.

Replace the Barrel The following table lists the steps to replace the barrel.

1 Pull back the retracting slide handle until the lug on the barrel locking spring is visible through the 3/8-inch hole in the right sideplate.
2 Place the smallest loop of a .50-caliber link between the trunnion block and the barrel extension. Note: If a link isn’t available, you can hold this alignment by hand.
3 Place the barrel into the front of the receiver and carefully start the threads.
4 Screw the barrel all the way in, then back it off two clicks.
5 Close the cover and remove the link if you used one.

Summary Assembling the components of the M2HB 50 caliber machinegun is just the first step of operator maintenance. The next step is to ensure that the weapon is properly assembled.

Schedule A function check of the M2HB .50-caliber machinegun ensures that the weapon is correctly assembled and should also be preformed before firing to ensure the weapon is in working order.

Important: You must set headspace and adjusting timing before conducting a function check.

Headspace Definition Headspace is the distance between the face of the bolt and the chamber when a round is fully seated in the chamber.

Setting Headspace Setting proper headspace is critical to operation of the M2HB .50-caliber machinegun. The correct headspace allows room for the rim of the round when chambered. The following table describes the results of incorrect headspace.

If the headspace is set too… Then…
Tight Firing will be sluggish and slow.
Loose Cartridge cases may bulge or even explode in the receiver.

Headspace To set headspace on the M2HB 50 caliber machinegun the operator needs the Gauge gauges shown below.

Setting Headspace Follow the steps in the table below to set headspace.

1 Ensure the gun cleared and the bolt is forward.
2 Pull back on the retracting slide handle until the locking spring lug aligns with the 3/8-inch hole on the right sideplate as shown in the picture below. Back barrel off two clicks from tight.
3 Grasp the retracting slide handle and pull the bolt to the rear, thus cocking the weapon.
4 Pull the bolt back 1/16-inch and raise the extractor arm up.
5 Insert the GO end of the headspace gauge between the face of the bolt and the chamber as shown below.
6 If the GO end Fits, go to step 7. Does not fit, go to step 8.
7 Turn the gauge over and try to insert the NO GO end. If the NO GO end Does not fit, headspace is correct. You have completed setting headspace. Fits, go to step 9.
8 Unscrew the barrel one click and repeat step 5.
9 Screw the barrel in one click and try to insert the GO end of the headspace gauge. Repeat step 6.
Timing Timing is achieved by adjusting the machinegun so that the moving parts do the right thing at the right time during the cycle of operation. Firing actually takes place just before the bolt is all the way forward. The machinegun must be adjusted to be sure this happens. Timing must be checked and adjusted each time headspace is set or when timing is questionable
Timing Gauges The picture below shows the placement of the timing gauges between the bolt and barrel assembly. In this case, the fire gauge has been inserted.

Preparing the Machinegun The operator must ensure the following items from the table below are completed before adjusting timing. Note: Timing must be checked every time headspace is completed.

1 Cock the machinegun
2 Ride the bolt slowly home
3 Raise the feed cover
4 Raise the extractor

Adjusting Timing After ensuring the weapon is prepared, perform the following steps from the table below to adjust timing.

1 Pull the retracting handle back until you have a ¼-inch space between the barrel extension and the trunnion block.
2 Insert the NO-Fire gauge between the barrel extension and the trunnion block with the beveled edge of the gauge resting on the barrel notches, as shown below:
3 Slowly let the barrel extension close by releasing the retracting slide handle.
4 Depress the trigger; and refer to the table below: If weapon does Then go to Not fire Step 16 Fires Step 5
5 Remove gauge and cock weapon.
6 Insert the Fire gauge, as stated in step 2.
7 Remove backplate.
8 Screw the timing adjustment nut, as shown in the picture below, to the left until it rests lightly on the trigger lever.
9 Turn the adjustment nut to the right one click.
10 With firm upward pressure, push up on the trigger lever as shown in the picture below.
11 Repeat steps 9 through 10 until the firing pin releases (fires).
12 When the firing pin releases, turn the timing adjustment nut two additional clicks to the right.
13 Replace the backplate and remove the FIRE gauge. WARNING: Never attempt to cock the machinegun with the backplate off.
14 Grasp the retracting slide handle, pull the handle back, and release it to cock weapon.
15 Repeat steps 2 through 4.
16 Insert the FIRE gauge.
17 Try to fire the machinegun by pressing the trigger. If the machinegun then fires, timing is correct, stop. Does not fire Go to step 6.

Function Check The operator must ensure the weapon is assembled properly. The table below lists the procedure to follow.

1 Place the weapon in single-shot mode.
2 Open the cover and lock the bolt to the rear.
3 Return the retracting slide handles to full forward position and press the bolt latch release.
4 Press down on the trigger. The weapon should fire.
5 Place the weapon in the automatic-fire mode.
6 Pull the retractor slide handle to the rear and release.
7 Make sure the firing pin does not protrude.
8 Press down on the trigger. The weapon should fire.
9 Make sure the firing pin does protrude.

Comments (11)

  • Richard Mooney


    During disassembly it should be noted to ensure that the bolt is in the forward position BEFORE you remove the back plate assembly as the drive spring has been known to fly out when the back plate clears it if the drive spring lock pin has broken off during operation. When this happens it is like having a spear gun fired into your belly if you make the mistake of sitting behind the weapon when you lift up on the back plate.


  • gm3 usnavy


    does anyone on here know how to lock the bolt to the rear when it is in full auto? it is one of the advanced functions of the m2hb. any help would be appreciated, thanks!


    • Joshua Ortiz


      Weapon is not designed to lock to the rear in fully automatic mode.


    • Richard Mooney


      It will lock to the rear as long as your not pressing the bolt release. It can be fired full auto by either locking the trigger down with the buffer sleeve or depressing both the trigger and the butterfly at the same time. If your firing with the trigger locked down just release the bolt release and the bolt will lock to the rear ceasing it from firing or just release both the trigger and butterfly and again it locks to the


  • Reid Woodward


    Hey-Good job! This is so much easier to do than everything else I have read.Thank you—now I’ll take a fun break!


  • ashenafi


    components of machine gun


  • Kelly Swarthout


    Right after exploring a number of the web site blogposts on your internet site currently, and I genuinely like your approach involving blogging. My partner and i book-marked this in order to my book mark internet site record and may also be looking at again before long. Could you try out this site while efficiently as well as tell me what you think.


  • John Mathewson


    great site!!! your cycle of opps is wrong though. Cocking happens inbetween extracting and ejecting, not after ejecting.


    • lala gee


      cycle of operation atart from when you press the trigger


  • Cristal Nicolai


    I am now not certain the place you are getting your info, but good topic. I needs to spend a while studying more or working out more. Thanks for excellent info I was searching for this information for my mission.


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    I can’t though agree. I always wished to write in my site a product like that but I can imagine you’r faster.


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