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Components of the M249 Machine Gun

Major Components, Sights and Safety with photos
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.

M249 Machine Gun Components

Sights.  The M249 machine gun has a hooded and semifixed front sight. 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 onehalf- 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-halfmil 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.

M249 Machine Gun Sights

Safety.  The safety 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.

M249 Machine Gun Safety