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Firinq mechanism block assembly |
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|  MIL-C-45975B(AR)
To close the breech, an upward force on the handles, assisted by the spring force
of the counterbalance assembly, shall swing the breechblock assembly up to the
point where the block lock disengages and the upper handle caroming surface
contacts the breech ring cam to initiate counter-clockwise rotation of the
breechblock and engagement of the sectored threads. Continued counterclockwise
rotation to the point where the cam plate inner stop surface contacts the housing
assembly shall bring the breech block assembly into the fully closed position.
In this position, the handle release lever shall engage the locking dowel.
3.4.2 Firinq mechanism block assembly. As the breechblock assembly is rotated
clockwise to open, the firing mechanism block assembly shall be automatially
caromed horizontally to the left. During this movement, the extractor arms shall
be actuated to forcibly eject the primer case from the primer chamber. When the
breechblock assembly is in the disengaged position, the firing mechanism block
assembly shall be removable by sliding the assembly horizontally to the right
while pulling outward on the cam follower.
As the breechblock assembly is rotated counterclockwise to close, the firing
mechanism block assembly shall be automatically caromed horizontally to the right
from the extract position to reach the primer load position as the breechblock
assembly reaches the fully closed position. When the breech is closed, the firing
mechanism block assembly shall be capable of being moved manually between the
load, the extract, and the firing positions.
3.4.3 Obturator group. The obrurator group functioning requirements shall
conform to MIL-C-393 ; however, the bearing requirements of obturator parts shall
apply when a force of 11,000 - 12,000 pounds is applied to the spindle in a
direction tending to compress the pad.
3.4.4 Firing mechanism. When assembled in the cannon, the firing mechanism
assembly shall cock and fire the primer as its lever is pulled by the attached
lanyard. When the lanyard is released, the mechanism shall position itself for
the next cycle.
3.4.5 Primer headspace. Primer headspace, the distance between the front face of
the firing mechanism block assembly and the rear face of the obturator spindle,
shall not be less than 0.062 inch nor more than 0.074 inch.
3.4.6 Firing pin protrusion and retraction. The firing pin protrusion measured
from the front face of the firing mechanism block shall be not less than 0.102
inch nor more than 0.119 inch in the fired position. Firing pin retraction behind
the front face of firing mechanism block shall be not less than 0.004 inch.
3.4.7 Thermal warning device. The requirements for the thermaal warning device
are specified in Appendix A (see 30.4).
3.5 Performance.
3.5.1 High pressure resistance. The cannon, spare tubes and muzzle brakes0 shall
0
be capable of withstanding a chamber pressure of 59,000 2,300 pSi at 70 + 3 F.
4
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