UNO serial number 0409
UNO proper shipping name Fuzes, detonating
The aluminum fuze head contains a spring-loaded striker and firing pin. A spring-loaded cylindrical slider, mounted transversely in the aluminum fuze body, contains the detonator and is equipped with an O-ring pressure seal. Inbore safety is provided by a spring-loaded bore riding pin which locks the slider. A pull wire restrains the setback pin (not shown in illustration) which locks the bore riding pin. Tape and a plastic disk protect the metering orifice. The fuze base contains a tetryl booster lead charge and a small tetryl booster charge.
Setback force from weapon firing forces the setback pin rearward against the pin spring and releases the bore riding pin. The bore riding pin then contacts the bore of the mortar and is ejected when the cartridge leaves the muzzle. Ejection of the bore riding pin unlocks the slider. The slider is moved by a compression spring, and because of the O-ring seal, a vacuum is formed behind the slider. The vacuum is relieved gradually by the bleed air orifice. The metered pressure relief through the orifice provides 1.5 to 6 seconds delay before the slider completes the movement necessary to align the detonator with the firing pin and arm the fuze. On impact, the striker and firing pin are depressed, and inertia throws the slider with detonator forward into the firing pin and arm the fuze. On impact, the striker and firing pin are depressed, and inertia throws the slider with detonator forward into the firing pin. Detonation is on superquick action through the booster lead charge and tetryl booster charge.
Refer to complete round for upper and lower limits.
Detonator tetryl booster lead charge, and tetryl booster charge.
TM 9-1015-215-10 TM 9-1300-251-20 SC1340/9t3-IL
C & T AMCTC 9193 dtd 1972.
Point Detonating Fuze M720 is of the superquick type used with 152mm gun Cartridge M657 and functions on impact or graze.
The fuze is essentially Fuze M557 modified to provide arming at closer than normal range and to assure superquick or non-delay detonation upon impact or graze. A superquick element in the head consists of a firing pin, firing pin support, and Detonator M24. The body of the fuze is a thin-wall ogive containing non-delay inertial type Plunger Assembly Ml. No optional delay setting is provided; the fuze as issued is preset on superquick. Booster M125A1 has been modified for use with Fuze M720 to reduce the normal arming distance to not less than 25 feet. The booster has a brass body inter nally threaded to accept the fuze body and externally threaded to fit Cartridge M657. A 340-grain tetryl booster charge is contained by an aluminum cup threaded onto the base of the booster. The tooster body contains Detonator M17 and a spin-activated mechanism to provide the delayed arming safety.
No action occurs until the projectile has left the muzzle of the gun, when the centrifugal force of rotation is high enough to move the interrupter outward and open the flash tube. At the same time, non-delay Plunger Assembly M1 is armed in reparation for impact by withdrawal of the plunger pins, also by centrifugal force. The rotation also starts movement of the rotor in the booster safety arming mechanism. The movement is so timed that Detonator M17 will be aligned with the flash holes when the projectile is not less than 25 feet from the muzzle. On impact, the superquick action will detonate the projectile. On graze, or in event of failure of the superquick element, detonation will be initiated by non-delay Plunger Assembly M1.
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