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Illumination Mortar Fuze M721
Type Classification:


This fuze is used on the 60mm illumination cartridge, M721.


The fuze is designed for a base ejection type round. The fuze has a mechanical arming/timing device and a black powder expulsion charge. The fuze can be set to function between 6 to 52 seconds of flight.


Upon setting of fuze, the setback sleeve is locked in place by the safety wire/pin. Removal of the safety pin allows the setback sleeve to move rearward. Setback force retracts the setback sleeve when the fuzed cartridge is pro-

Eelled up the mortar barrel. The retracted set-ack sleeve allows the locking balls to move inward and the setback pins to move rearward. A V-spring locks the setback pins in the rearward position. The escapement lever and gears of the mechanical arming/timing device are released. The gears rotate the rotor release shaft. During setback, the firing pin is driven temporarily rearward into a blind hole in the rotor: this prevents the rotor from being prematurely released until the cartridge has left the mortar barrel. The rotor is released when the grooves in the setback pins are aligned with the flange of the rotor and the end of the rotor release shaft is disengaged from the slot in the rotor. The rotor rotates to the armed position where the detonator is aligned with the firing pin. The mainspring turns the mainspring barrel. The release lever disengages from the firing lever, when the firing lever engages a slot In the mainspring barrel. Disengagement of the release lever from the firing lever allows the striker to impact the firing pin. The firing pin stabs the detonator. The detonator initiates the black powder expulsion charge. The expulsion charge ejects the payload. The time of ejection can he set/varied prior to firing by rotating the head of the fuze: this adjusts the starting position of the firing lever (relative to the slot in the mainspring barrel) and the required degree of rotation. The fuze functions on impact should the timing device fail or the set time exceed the time of flight.

Tabulated Data:

M776 Fuze.

Complete Round:

Type ------------------------------- Mechanical time superquick

We'8ht 0.50 lb t (0.23 kg) Length ------------------------------ 3,44 in.

Intrusion --------------------------- 1.08 in. (2.74

Drawing number 12361000

Temperature Limits;


Lower ------------------------------- -50°F (-45.5°C)


(for a period of not more than

3 days)

(+71.1C°) (for a period of not more than 4 hr/day)

Shipping and Storage Data

DOD hazard class (04) 1.2

Storage compatibility group — B

DOT shipping class C


Limitations: None.


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