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    AV-1 d/u bomb fuze, Russia, WW2 and post WW2

    Cutaway model of a Russian AV-1 d/u bomb fuze. This fuze is used in the FAB-250 M46 high explosive bomb as nose or tail fuze.
    The fuze is an impact activated, all ways , pyrotechnic delayed fuze.

    The fuze consists of a fuze head, which houses the threaded arming stem with the arming vane on top. A radial placed limiting pin at the base of the thread through the arming stem, stops the arming vane from falling out of the fuze when fully armed. The inside of the fuze head is chamfered.

    The fuze body screwed to the base of the fuze head houses the all-ways fuze parts. These are the brass firing pin carrier and the brass primer carrier. These are held apart by a creep spring when armed, and by two lock balls when in safe position. Below the primer carrier a loose ring with a chamfered inside is placed.

    In the lower part of the fuze body the pyrotechnic delay pellet is placed. Above this pellet, a flash channel, a bypass channel and a channel sealing screw are placed, allowing for two different delay settings.
    Into the base of the fuze body the booster with a detonator in top is screwed.
    To change the fuze from nose to tail fuze the blades of the arming vane are to be bend in the prescribed attitude for tail fuze. This is done before placing the fuze in the bomb.

    Functioning of the fuze:
    Upon release from the bomb rack, the safety fork is withdrawn from the fuze body, allowing the arming vane to rotate in the airstream. With ten rotations of the arming stem, the fuze will react on direct impact (two locking balls have fallen inward). With thirty seven revolutions the fuze will function upon graze impact.

    When used as nose fuze upon impact: the primer carrier will be thrown forward by inertia –riding the creep spring, pushing the primer (red) into the firing pin
    When used as base fuze upon impact: the firing pin carrier will be thrown forward by inertia –riding the creep spring, pushing the firing pin into the primer (red).
    Upon graze, the rounded surfaces of the firing pin carrier and the primer carrier are thrown downward together, forcing them to move towards one another when moving down the chamfered edges, pushing the firing pin and primer together, exploding the primer (red).

    Below the all ways fuze a channel sealing screw is placed; when screwed in, the long delay is used (green arrow in pict.03), as the flame from the primer follows the long pyrotechnic channel in the pyrotechnic delay pellet (pict 04). When unscrewed (yellow arrow, pict 03), the flame follows the bypass channel (red arrows) , shortening the pyrotechnic delay channel by half (purple arrow). Long delay is between 22,5 and 31 seconds, short delay between 11 to 16 seconds. The channel sealing screw is set before inserting the fuze into the bomb.

    The flame appearing from the base of the pyrotechnic delay pellet ignites the detonator, which ignites the booster charge.

    The Czech manual Let-4-1/1 (1966) lists some other possibilities for the use:
    FAB-250 M54
    FAB-500 M54
    FAB-1000 M54
    FAB-1500 M54
    FAB-3000 M54
    FAB-5000 M54
    FAB-9000 M54
    FAB-250 ts
    FAB-500 ts
    FAB-1500-2600 ts
    FAB-250 M46
    FAB-500 M46
    FAB-3000 M46
    OFAB-100 nv
    By this time it was used with the MDV-5 delay safety mechanism (1,9 ± 0,4 sec).
    I guess there was more types in Russia

    Period 2WK :

    FAB-250 M-43
    FAB-250 M-44
    FAB-500 M-43
    FAB-500 M-44
    FAB-1000 M-44

    ZAB 100ck

    Regards, DJH
    Attached Images Attached Images

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