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Operation and Function of the M203 Grenade Launcher (FM 3-22.31)




The grenadier’s
operations include loading, unloading, and firing
the weapon. The weapon uses a high-low propulsion
system to fire a 40-mm round. The firing pin
strikes the primer, whose flash ignites the
propellant in the brass powder-charge cup inside
the high-pressure chamber. The burning propellant
produces 35,000 psi chamber pressure, which
ruptures the brass powder-charge cup at the vent
holes and allows the gases to escape to the
low-pressure chamber in the cartridge case. There
the pressure drops to 3,000 psi and propels the
grenade from the muzzle at a velocity of 250 fps.
The grenade’s 37,000-rpm right-hand spin
stabilizes it during flight and applies enough
rotational force to arm the fuze. The weapon is
unloaded with the barrel open and fired from a
closed bolt. It must be cocked before it can be
placed on SAFE.




To load the
weapon, the grenadier must first press the barrel
latch and slide the barrel forward. Once the
barrel is in the forward position, the grenadier
places the weapon on SAFE and visually inspects
the barrel to ensure it is clear. Then he inserts
clean, dry, undented ammunition into the chamber
and slides the barrel rearward until it locks with
an audible click (Figure 2-1).

Figure 2-1. Loading the M203 grenade launcher.

Figure 2-1. Loading the M203 grenade launcher.



Keep the
muzzle pointed downrange and clear of
all soldiers.

Use the
correct ammunition: never use high-velocity
40-mm ammunition designated for other 40-mm
weapons such as the MK 19. High-velocity
rounds are longer than those used in the M203
and may cause this weapon to explode.





To unload the
grenade launcher, the grenadier must first depress
the barrel latch and move the barrel forward. The
cartridge case or round should automatically
eject. If the case is stuck, he taps it with a
cleaning rod to remove it (Figure
2-2). He places the weapon on SAFE, then
slides the barrel rearward, locking it to the

Figure 2-2. Unloading the M203 grenade launcher.

Figure 2-2. Unloading the M203 grenade launcher.



If you are
unloading a weapon that has not been fired,
avoid detonation either by catching the
ejected round or by holding the weapon close
to the ground to reduce the distance the round
can fall.



2-4.  CYCLE OF


Knowing the
M203’s cycle of functioning from loading to firing
helps grenadiers recognize and correct stoppages.
Many of the actions described in this chapter
occur at once, but here they are explained

a.  Unlocking.
The cycle begins when the grenadier depresses
the barrel latch to unlock the barrel assembly
and slides the barrel assembly forward (Figure

Figure 2-3. Unlocking the barrel assembly.

b.  Cocking.
The grenadier moves the barrel assembly forward,
then backward, to cock the weapon. As the barrel
assembly moves, it takes with it the barrel
extension. Their movement causes the following
to occur:

(1)  The
cocking lever is forced down as the barrel
assembly and barrel extension, which are
interlocked with the cocking lever, move

(2)  The
movement of the cocking lever forces the
spring-loaded firing pin to the rear.

(3)  The
spring-loaded follower also moves forward with
the barrel extension.

(4)  The
barrel assembly continues forward, disengaging
the barrel extension from the cocking lever.
The cocking lever is then held down by the

(5)  When the
grenadier begins to move the barrel assembly
back to the rear, this forces the follower to
the rear.

(6)  The
cocking lever again engages the barrel
extension, which causes the firing pin to move
slightly forward and engage the primary
trigger sear. This cocks the weapon (Figure

Figure 2-4. Cocking the M203 grenade launcher.

c.  Extracting.
Extracting and cocking occur at the same time.
As the grenadier opens the barrel assembly, a
spring-loaded extractor keeps the live round or
spent cartridge case seated against the receiver
until the barrel clears the cartridge case (Figure

Figure 2-5. Extracting the round or cartridge case.

Figure 2-5. Extracting the round or cartridge

d.  Ejecting.
The spring-loaded ejector pushes the live round
or spent cartridge case from the barrel assembly
(Figure 2-6).

Figure 2-6. Ejecting the round or cartridge case.

Figure 2-6. Ejecting the round or cartridge case.

e.  Loading.
With the barrel assembly open, the grenadier
inserts a round into the breech end of the
barrel (Figure 2-7).

Figure 2-7. Loading the M203 grenade launcher.

Figure 2-7. Loading the M203 grenade launcher.

f.  Chambering.
As the grenadier closes the breech end of the
barrel assembly, the extractor contacts the rim
of the cartridge and seats (chambers) the round
firmly (Figure 2-8).

Figure 2-8. Chambering a round.

Figure 2-8. Chambering a round.

g.  Locking.
As the barrel assembly closes, the barrel latch
engages it. The cocking lever engages the barrel
extension so that it cannot move forward along
the receiver assembly.

h.  Firing.
When the grenadier pulls the trigger, the
primary trigger sear disengages from the bottom
sear surface of the firing pin. This releases
the spring-driven firing pin, forcing it forward
against the cartridge primer (Figure

Figure 2-9. Firing the M203 grenade launcher.