Specifications

TM 05539-IN

0003 00-1

PRINCIPLES OF OPERATION 0003 00

GENERAL DESCRIPTION

1. Cycle of Operation

. Knowledge of what happens during the cycle of operation will help the operator understand the

cause of and remedy for various stoppages.

2. Eight Steps

. The cycle of operation consists of eight steps:

a. Firing

b. Unlocking

c. Cocking

d. Extracting

e. Ejecting

f. Feeding

g. Chambering

h. Locking

3. Description of Eight Steps. These eight steps are explained below, including a brief description of what occurs inside

the weapon during each step. Assume that a full magazine is loaded in the weapon, that the first cartridge is chambered,

and that the bolt is forward and locked.

a. Firing. The trigger with attached connector pivots on the trigger pin, allowing the sear safety cam to drop down

and release the firing pin. The firing pin under spring tension is propelled forward to strike the primer of the car-

tridge. The primer ignites the powder inside the cartridge case and gas pressure builds. The building gas pressure

exerts thrust on the face of the bullet, pushing it against the lug abutments while propelling the bullet down and out

of the bore at the same time.

b. Unlocking. After firing, the operator starts to rotate the bolt handle up, which unlocks the bolt from the breech.

c. Cocking. When the bolt handle is lifted, the firing pin cap is cammed into the notch of the bolt body.

d. Extracting. The bolt handle, while still being

lifted, contacts the primary extraction surface on

the rear of the receiver, which provides mechani-

cal leverage to initially break the seal of the car-

tridge inside of the chamber and start the

rearward movement of the bolt to the rear. The

extractor (1), being engaged with the extraction

rim of the cartridge case, pulls the spent case

from the chamber.

e. Ejecting. The bolt, while continuing its rearward

motion in the receiver, continues to pull the spent

cartridge case until it clears the ejection port. As

soon as the spent cartridge clears the ejection

port, it is expelled from the weapon by the ejec-

tor (2), which is under spring tension. The bolt

continues to the rear until it makes contact with

the bolt stop inside the receiver.

M40-2003