a certain sequence. The sequence of operation is known
Check the gas system to ensure that the gas-port plug,
as the cycle of functioning.
gas-cylinder extension, and gas-cylinder nut are tight.
Clean the operating rod tube. Replace parts as necessary.
The cycle of functioning is divided into eight basic
steps that are listed below in the order they occur;
however, more than one step may occur at the same time.
STOPPAGES
FEEDING--A round is positioned into the feed tray
groove.
A stoppage is any interruption in the cycle of
CHAMBERING--A round is stripped from the belt
functioning caused by a faulty action of the gun or
and placed in the chamber.
ammunition. Stoppages are classified by the
relationship to the cycle of functioning. Table 13-1
LOCKING--The bolt is locked inside the barrel
shows the types of stoppages, their causes, and the
socket.
corrective action to be taken.
FIRING--The firing pin strikes and detonates the
primer of the cartridge.
IMMEDIATE ACTION
UNLOCKING--The bolt is unlocked from the barrel
socket.
EXTRACTING--The empty case is pulled from the
Immediate action is the action taken to reduce the
chamber.
stoppage without investigating the cause. This action
must be accomplished within 10 seconds, including
EJECTING--The empty cartridge case is thrown
waiting time, when the barrel is hot enough to cause a
from the receiver.
cook off. A cook off is the ignition of a round caused by
COCKING--The sear engages the sear notch.
the heat of the chamber without the firing pin striking
the primer of the cartridge. One hundred and fifty rounds
MALFUNCTIONS
fired in a 2-minute period may heat the barrel
sufficiently to cause a cook off.
A malfunction is a failure of the gun to function
If a stoppage occurs, wait 5 seconds. (The bolt must
satisfactorily. Defective ammunition or improper
remain forward for the first 5 seconds because of the
operation of the gun by either you or one of your crew
possibility of a hangfire.)
members is not considered a malfunction of the gun.
Two of the more common malfunctions of the M60
After the 5-second wait, raise the cover and remove
machine gun are sluggish operation and a runaway gun.
the ammunition belt and the links from the feed tray.
Sluggish operation of the gun is usually caused by
Pull the cocking handle to the rear, making sure the
excessive dirt or carbon, lack of proper lubrication,
sear engages the sear notch in the operating rod; close
burred parts, or excessive loss of gas. Clean and
the cover immediately; then return the cocking handle
lubricate the gun; inspect for burred parts and have them
to its forward position.
replaced as necessary by the armorer. Excessive loss of
gas is usually caused by a loose or missing gas-port plug.
During the retraction of the bolt, observe the round
being extracted and ejected. If the round is NOT
The best method of stopping a runaway gun depends
extracted, pull the trigger, attempting to fire the round.
on many factors. Some of these factors are the amount
If the round does not fire and the barrel is hot, wait at
of ammunition remaining in the belt, how the gun is
least 5 minutes with the bolt in the forward position to
mounted, and whether an assistant gunner is present. For
prevent damage or injury to personnel in the event of a
example, in assault firing with the bandoleer attached to
cook off. After the 5-minute wait, remove the round by
the gun, you will continue to move forward, keeping the
using a cleaning rod inserted from the muzzle end of the
gun on target until the ammunition is expended. In other
gun.
types of firing, the primary consideration is keeping the
gun on target; however, either you or the assistant
When the round is extracted or when a round is
gunner may be able to stop the gun by twisting or
removed from the chamber, inspect the gun and
breaking the belt to stop the feeding.
ammunition to determine the cause of the stoppage.
When you have ceased firing the gun, field-strip it
After cleaning the machine gun, reload, rezero in on
and check the sear and sear notch for excessive wear.
the target, and attempt to fire.
13-10
