Operation and Cycle of Functioning

OPERATION

The M60 machinegun is loaded, fired, unloaded, and cleared from the open-bolt position. The safety lever must be placed on FIRE before the bolt can be pulled to the rear.

Before using ammunition, insure that

# It is properly linked.

• It is free of dirt and corrosion.

9 The double link is at the opening end of the bandoleer.

LOADING

Place the safety lever on FIRE. Pull the bolt to the rear by the cocking handle with the palm facing UP. When the bolt is held to the rear by the sear, manually return the cocking handle to the forward position and place the safety lever on SAFE. Raise the cover and insure that the tray, receiver group, and chamber are clear. Place the first round of the belt in the tray groove, double link leading, open side of links down. INSURE THAT THE ROUND REMAINS IN THE TRAY GROOVE, AND CLOSE THE COVER. Hold the belt up, approximately six rounds from the loading end, while closing the cover.

TRAY UNLOADED

Inside The M60 Feed Cover
4-1

TRAY LOADED

DOUBLE LINK

BOLT

DOUBLE LINK

BOLT

M60 Operation

UNLOADING AND CLEARING

Pull the bolt to the rear, if it is not already there. Place the safety lever on SAFE and manually return the cocking handle to its forward position. Raise the cover and remove any ammunition or links from the tray. Look in the chamber to insure that it is clear. Clearing procedure is covered in chapters 2 and 5.

CYCLE OF FUNCTIONING

Crew members can recognize and correct stoppages when they know how the gun functions. The gun functions automatically as long as ammunition is fed into it and the trigger is held to the rear. Each time a round fires, the parts of the gun function in sequence. Many of the actions occur at the same time and are separated only for teaching purposes. The sequence of functioning is known as the CYCLE OF FUNCTIONING. As a "minimum" standard, the soldier should know the eight basic terms and short definitions in the paragraph below.

STEPS OF THE CYCLE

The complete cycle of functioning is taught in eight separate steps, as follows:

(1) Feeding. A round is positioned in the feed-tray groove.

(2) Chambering* A round is stripped from the belt and placed into the chamber.

(3) Locking. The bolt is locked inside the barrel socket

(4) Firing* The firing pin strikes and fires the primer, which fires the cartridge.

(5) Unlocking, The bolt is unlocked from the barrel socket.

(6) Extracting. The empty cartridge case is pulled from the chamber.

(7) Ejecting. The empty cartridge case is thrown from the receiver.

(8) Cocking. The sear engages the sear notch on the operating rod.

Start the cycle by putting the first round of the belt in the tray groove. Then, pull the trigger, releasing the sear from the sear notch. When the trigger is pulled to the rear, the rear of the sear is lowered and disengaged from the sear notch. This allows the operating rod and bolt to be driven forward by the expansion of the driving spring. The cycle stops when the trigger is released and the sear again engages the sear notch on the operating rod.

SEAR DISENGAGING FROM

SEAR NOTCH

BOLT

BOLT

OPERATING ROD

SEAR NOTCH

TRIGGER

SEAR

OPERATING ROD

SEAR NOTCH

TRIGGER

SEAR

SEQUENCE OF FUNCTIONING

Feeding\ As the bolt starts its forward movement, the feed cam is forced to the right, causing the feed-cam lever to turn in the opposite direction. This forces the belt-feed pawl over the next round in the bolt, and it is ready to place the next round into the tray groove when the rearward action occurs again.

As the bolt moves to the rear after firing, the cam roller forces the feed cam to the left. The feed-cam lever is forced to turn, moving the feed pawl to the right, and this movement places a round in the tray groove.

Chambering. As the bolt travels forward, the upper locking lug engages the rim of the round. The pressure of the front and rear cartridge guides holds the rounds so that positive contact is made with the upper locking lug of the bolt. The front cartridge guide prevents forward movement of the link as the round is stripped from the belt.

BOLT CONTACTING CARTRIDGE

UPPER LOCKING LUG

HOUND IN FEEDTRAY GROOVE

UPPER LOCKING LUG

HOUND IN FEEDTRAY GROOVE

Locking Cycle

BOLT MOVIN FORWARD

LOWER LOCKING LUG

BOLT MOVIN FORWARD

LOWER LOCKING LUG

The upper locking lug carries the round forward. The chambering ramp causes the nose of the round to be cammed downward into the chamber.

ROUND BEING DEFLECTED INTO CHAMBER

80LT MOVING FORWARD

HAM BERING RAMP (RECEIVER)

80LT MOVING FORWARD

HAM BERING RAMP (RECEIVER)

M60 Operating Rod

OPERATING-ROD YOKE HELD TO THE REAR OF THE BOLT CAMMING SLOT

BOLT LUGS HELD IN VERTICAL POSITION BY CHANNEL IN TOP OF RECEIVER

OPERATING-ROD YOKE HELD TO THE REAR OF THE BOLT CAMMING SLOT

BOLT LUGS HELD IN VERTICAL POSITION BY CHANNEL IN TOP OF RECEIVER

When the round is fully seated in the chamber, the extractor snaps over the rim of the round, and the ejector on the face of the bolt is depressed.

Locking. As the round is chambered, the bolt enters the barrel socket. The upper and lower locking1 lugs contact the bolt camming surfaces inside the barrel and start turning

BOLT FORWARD

RETUR

FEED CAM

BELT-FEED

M240 Feed Assembly

FEED-CAM LEVER

POSITION OF CAM ROLLER

BOLT TO REAR

BOLT TO REAR

FEEDING

BOLT FORWARD

BELT-FEED

FEED-CAM LEVER

RETUR

FEED CAM

POSITION OF CAM ROLLER

the bolt clockwise. The action of the operating-rod yoke against the bolt-camming slot, as the operating rod continues forward, turns the bolt to complete its 90-degree (one-quarter turn) clockwise rotation- Locking is now complete.

GUN LOCKED, READY TO FIRE

RIGHT AND LEFT BOLT CAMMING SURFACES IN BARREL SOCKET

RIGHT AND LEFT BOLT CAMMING SURFACES IN BARREL SOCKET

Forward Ejection Machine Gun

Firing. After the bolt is fully forward and locked, the operating rod continues to go forward, independent of the bolt, for a short distance. The yoke, engaged between the firing-pin spools, carries the firing pin through the opening in the face of the bolt The firing pin strikes the primer of the round, and the primer fires the round.

FIRING AND COCKING

FIRING PIN SPOOLS

FIRING PIN

FIRING PIN SPOOLS

FIRING PIN

M60 Rod Guide

OPERATING-ROD OPERATING ROD

YOKE

OPERATING-ROD OPERATING ROD

YOKE

Unlocking* After the round is fired and the bullet passes the gas port, part of the expanding gases go into the gas cylinder through the gas port. The rapidly expanding gases enter the hollow gas piston and force it to the rear. The operating rod, being in contact with the piston, is then forced to the rear.

ACTION OF GASES

PISTON

GAS PORT

PISTON

GAS PORT

Browning Gas Ports

OPERATING

rod GAS

ESCAPE HOLE

PLUG

ESCAPING THROUGH BLEEDER HOLE

OPERATING

rod GAS

ESCAPE HOLE

PLUG

ESCAPING THROUGH BLEEDER HOLE

As the operating rod continues to the rear, the operating-rod yoke acts against the bolt-camming slot. This causes the bolt to begin its counterclockwise rotation. The upper and lower locking lugs of the bolt contact the bolt-camming surfaces inside the barrel socket, and, as the bolt continues to the rear, it completes a one-quarter turn counterclockwise. The rotation and movement to the rear unlocks the bolt from the barrel socket. Unlocking begins as the yoke of the operating rod contacts the curve of the bolt-camming slot, and ends as the bolt clears the end of the barrel socket.

Extracting. Extracting begins during the unlocking cycle. The rotation of the bolt loosens the cartridge case in the chamber.

EXTRACTION AND EJECTION

BOLT

EJECTOR

BOLT

EJECTOR

Casing Extraction And Ejection Marks

EXTRACTOR

EJECTION PORT

EXTRACTOR

EJECTION PORT

As the operating rod and bolt move to the rear, the extractor pulls the cartridge case from the chamber.

Ejecting. As the cartridge case is pulled from the chamber, the ejector spring expands. This causes the ejector to press on the base of the spent case, forcing the front of the case against the right side of the receiver. As the bolt continues to the rear, the action of the ejector pushing against the base of the cartridge case and the extractor gripping the right side of the case causes the cartridge case to spin from the gun as the case reaches the ejection port. The empty belt links are forced out of the ejection port as the rearward movement of the bolt causes the next round to be positioned in the tray groove.

Cocking. As the expanding gases force the gas piston to the rear, the operating rod first moves independently of the bolt. The yoke of the operating rod acts against the rear firing-pin spool, pulling the firing pin from the primer of the spent cartridge case. The action of the operating-rod yoke, continuing to the rear against the rear firing-pin spool, fully compresses the firing-pin spring.

As long as the trigger is held to the rear, the M60 will continue to complete the right steps of functioning automatically. When the trigger is released and the sear again engages the sear notch, the cycle of functioning is stopped and the gun is cocked. To prevent undue wear to the sear and sear notch, the gunner must hold the trigger firmly to the rear during firing.

CHAPTER 5

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