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Mechanical Time and Superquick (MTSQ) Fuze M577A1/M577 is used with , 105mm cartridges, 155mm, and 8-inch projectiles. It is used with projectiles carrying payloads that are expelled during projectile flight (airburst). The fuze contains a mechanical clockwork timing mechanism that can be set to function at any time from 2 to 200 seconds. The fuze is set with M35 fuze setter or flat screwdriver. The setting key is at the nose of the fuze, and the time to be set is viewed on three dials through a window in the side of the ogive. The dial closest to the nose indicates hundreds of seconds, or a triangle for a non-time setting. The second dial indicates tens of seconds, and the third dial indicates seconds and tenths of seconds. All setting are made by reference to a hairline visible through the window The timing mechanism and point detonating element are contained in the ogival nose section of the M577. The M577A1 does not contain the point detonating element, but rather utilizes the safe separation assembly as an inertial element to initiate impact function. On impact, the safe separation assembly slides forward and the detonator in the rotor is stabbed by the firing pin in the trigger mechanism. The safe separation device and trigger are contained in the fuze body. The timing mechanism and safe separation assembly are prevented from operating before adequate projectile spin is attained by centrifugally operated lock pins and the centrifugal detents are further restrained by setback pins. The safety and arming mechanism includes a spin-activated rotor to block the detonation train prior to arming. Movement of the arming mechanism is interlocked by a scroll fol- lower in the timing mechanism, which also restrains the firing pin. The M577 fuze has an aluminum ogive with an anodized black coating and a steel lower body. The M577A1 fuze has a zinc ogive but earlier manufactured A1 fuzes have black paint coated ogives while later manufactured A1 fuzes have chromate finished (gold color) ogives. The M577A1 ogive also has different wrench slots though the same wrench is used. The lower body is aluminum with chromate coating. Setback and centrigual forces from weapon firing acting on spring, lock, and spin detents allow the fuze to arm and function at its preset time or if the setting is point detonating, on impact with the target. The safe separation device is designed to provide the safety and arming features of the fuze. A rotor, which carries a detonator, is held out of line with respect to the firing pin by two spin detents, and further restrained by the interlock in the trigger, A properly sequenced firing environment (setback and spin) will actuate the interlock and detents allowing the rotor to rotate to the inline (ARMED) position. When the setting is point detonating, or for a time less than 4 seconds, the rotor is released almost immediately. However, when set for a longer time, the rotor is not released by the interlock until approximately 3 seconds before the set time, thus providing overhead safety (because of this delay, when the fuze is set for airburst and the projectile impacts before the time setting, the fuze may not function). Motion of the rotor is controlled by a runaway escapement with its arming distance dependent on the subjected spin rate. Spin rate is a function of the characteristics of the weapon/propelling charge combination. A difference in functioning must be noted in the point detonating mode between the M577A1 and the M577. On impact, a point detonating element in the nose initiates the explosive train of the M577 fuze. For the M577A1 fuze, on impact the safe separation device will shale forward and the rotor detonator will be stabbed by the firing pin in the trigger mechanism to activate the explosive train of the fuze. Our fuze shown in the video is inert.
