And Maintenance


10-1. General

This chapter contains instruction for mechanical training, operation and functioning of the 40-mm grenade launcher, M79.

10-2. General Disassembly

Grenadiers are authorized to disassemble the launcher as follows :

a. Clear the weapon by rotating the barrel lock-

M79 Bolt Screw For Butt
Figurt 10-1. Removing or installing the retaining band screw.

ing latch lever its full travel to the right and opening the barrel. Inspect the breech to insure that no round is present.

b. Remove the sling from the stock.

c. Remove the retaining band screw, which passes through the rear mounting of the front sling swivel, and pull the fore-end assembly away from the barrel (fig 10-1 and 10-2).

d. Press the barrel locking latch lever to the right; pivot the barrel down until it stops; slide the barrel off the fulcrum pin and remove it from the receiver (fig 10-3). Do not remove the rear sight from the barrel.

e. Remove the stock screw and washers and pull the stock rearward from the receiver (fig 10-4).

10-3. Assembly

Assembly of the grenade launcher is the reverse of disassembly.

a. Place the stock on the receiver and replace the stock screw and washers. Place the lock-washer on the stock screw first.

b. Place the barrel on the fulcrum pin (fig 10-5). Hold the cocking lever up, lower the barrel, and insure that the cocking arm slides under the cocking lever. Close the barrel.

c. Place the fore-end assembly on the barrel and secure it by replacing the retaining band screw.

d. Replace the sling.

M79 Grenade Launcher Parts


Figure 10-2. Removing or installing fore-end assembly.

M79 Grenade Launcher Parts

fulcrum pin

Figure 10-3. Removing or installing the barrel group.

Homemade M16a1


Figure 10-i. Grenade launcher, general disassembly cocking lever cocking lever

40mm Grenade Ammunition

Figure 10-5. Assembling barrel group and receiver group.

cocking arm fulcrum pin

Figure 10-5. Assembling barrel group and receiver group.


10-4. Preparation for Firing a. Check the bore to be sure it is clear and dry. Check the launcher to be sure it is clean.

c. Inspect for defective parts.

d. Insure that the firing pin retainer is tight (fig 10-6). Turn it clockwise with the combination tool. A loose firing pin retainer is the most probable cause for a failure to fire.

10-5. Functioning a. Unlocking (fig 10-7).

(1) Unlocking is done by pressing the barrel locking latch lever its full travel to the right. This unlocks the barrel from the receiver and moves the safety to the safe position.

(2) The barrel locking latch is held in the open position by a spring-loaded latch lock (fig 10-10).

(1) The weapon is cocked when the barrel is opened.

(2) As the barrel is opened the cocking arm lifts the cocking lever and causes it to rotate

Ruger Mkii Firing Pin
Figure 10-8. Position of firing pin retainer.

around the hammer pin contacting a stud on the hammer.

(3) The cocking lever rotates upward with the hammer until the sear notch is engaged by the sear.

(1) Extraction and cocking take place at the same time.

(2) As the barrel is opened, the spring-loaded extractor withdraws the spent cartridge case about 1/2 inch from the breech end of the barrel.

(1) The launcher is not equipped with an automatic ejector.

(2) To eject, manually remove the expended cartridge case or live round from the barrel.

e. Loading (fig 10-8). With the barrel in the open position the cartridge is inserted into the breech end of the barrel.

/. Chambering.



M79 Trigger Group Diagram

cocking arm

Figure 10-7. Unlocking, cocking, and extraction.

cocking arm

Figure 10-7. Unlocking, cocking, and extraction.

(1) Chambering takes place during the closing of the barrel.

(2) As the barrel is closed, the extractor iB forced into the extractor housing and the cartridge is seated into the chamber.

(1) As the barrel closes and the latch lock is depressed, the barrel locking latch rotates until it is engaged with the barrel locking lug.

(2) The barrel is now locked to the receiver and the launcher can be fired after the safety is pushed forward exposing the letter F.

(1) As the trigger is pulled rearward it rotates about the trigger pin and the rear of the trigger lifts the rear of the sear causing the nose of the sear to become disengaged from the sear notch in the hammer. This releases the spring driven hammer to strike the firing pin and drive it forward to strike the primer of the cartridge.

(2) As the trigger is released the hammer settles back slightly, allowing the firing pin to be withdrawn from the face of the retainer through the action of the firing pin spring.

10-6. Troubleshooting a. Stoppages and immediate action are as outlined in paragraph 3-6, 3-7, and 3-8.

b. Troubleshooting is the systematic study of trouble signs, testing to determine the defective components, and applying corrective action (chart 10-1).

40mm Grenade Launcher
Figure ÍO-3. leading or ejecting.

riRiNG PI*



riRiNG PI*


Trigger M79



Figure 10-0. Firing.



Figure 10-0. Firing.

Chart 10-1. Troubleshooting


Cormllv« Mtlon

Failure to fire

Failure to chamber

Failure to extract

Failure to cock

Safety fails to stay in selected position.

Rear sight will not stay in selected position

Safety in S position

Empty chamber

Loose firing pin retainer

Faulty ammunition

Short, worn, or broken firing pin.

Dirty firing pin opening

Broken hammer

Weak or broken hammer spring Broken sear, cocking arm, cocking lever

Faulty ammunition Dirty chamber

Defective extractor

Set or broken extractor spring

Ruptured cartridge case

Defective sear

Defective cocking arm or lever Broken or weak safety spring

Broken or weak sight lock spring Broken lug on sight lock

Place in F position. Load weapon. Tighten firing pin retainer. Reload.

Replace firing pin. Clean Aring pin opening. Turn in to armorer. Turn in to armorer. Turn in to armorer.

Reload. Clean bore.

Turn in to armorer. Turn in to armorer. Remove from barrel

Turn in to armorer. Turn in to armorer.

Turn in to armorer.

Turn in to armorer. Turn in to armorer.

M79 Armorers Manual


Maintenance of the M79 is the same as that for the M203 in chapter 5.

Authorized organizational maintenance is shown in chart 10-2.

Chart 10-t. Authorised Organinational Maintenance (M79)


Barrel group :

Cleaning and lubrication Pore-end assembly: Cleaning and lubrication Replace machine »crew . Receiver group : Cleaning and lubrication

Replace firing pin------------------------------—

Sight assembly:

Stock assembly:


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