5 Phases Of Function For The M256A1 Gun Tube

Front 1

Manual Opening

Back 1

(a) As the breech operating handle is rotated from the 5 o’clock position up ward toward the 12 o’clock position, the breech mechanical shaft is rotated counterclockwise.
(b) This movement brings the breech operating crank from its position of forward of Top Dead Center (TDC), breaking the mechanical lock.
(c) During the crank rotation, but before the breechblock begins to open, the crank moves past the driver, which protrudes from the bottom of the sliding block. This action allows the driver to drop down into the slot on the breech operating crank. This action releases pressure on the firing pin, which allows the firing pin to retract.
(d) Further rotation of the breech mechanical shaft allows the breech block to open, compressing the breech spring mechanism.
(e) As the breech block approaches the fully open position, the extractors are forced to rotate to the rear by the extractor plunger and spring exerting pressure on the extractor shaft. The extractors moving up the inclined face of the breechblock allow the extractor plunger and spring to expand, rotating the extractor shaft. This action forces the locking shoulders of the extractors to engage the seats on top of the breech block. The breechblock is locked in the open position.

Front 2

Automatic Closing

Back 2

As the round is loaded, the rim of the case base strikes both lips of the extractors. This causes the extractor shoulders to rotate off their seats on top of the breechblock. The spring mechanism is allowed to reassert stored energy, rotating the breech mechanical shaft, forcing the breechblock upward. As the breechblock closes and the crank moves over TDC, the breech operating crank rotates against the sliding block. As the breech operating crank rotates against the sliding block, the crank pushes the driver upwards, which extends the firing pin.

Front 3

Firing

Back 3

(a) The case base is grounded by the grounding pin located on the face plate of the breechblock.
(b) When the triggers are pulled, electrical current travels from the turret networks box (TNB) through the wiring harness to an electrical contact located on the gun mount (1W108-E2). When the gun is in battery this contact touches an electrical contact on the breechring. Electrical current passes through this electrical contact and along a wire lead located on the side of the breech ring. This wire lead is connected to another firing contact that passes through the side of the breechring to make contact with another electrical contact located on the side of the breech block.
(c) The electrical contact in the breech block passes through the side of the breechblock and touches an electrical contact located on the side of the firing pin. Electrical current passes through these electrical contacts, through the firing pin, to the primer of the round, where it is ignited.

Front 4

Automatic Closing

Back 4

(a) When the round is fired the same force that propels the round towards the target also pushes the gun to the rear, this is known recoil.
(b) The breech stays closed and locked during recoil. As the gun recoils, the lug on the operating lever bears against the inner face of the operating cam, forcing it to the right. When the lug on the breech operating lever is clear of the breech operating cam, a spring on the rear of the breech operating cam arm pushes the operating cam to the left towards the breechring. The operating cam on the operating cam arm is now in the path of the lug of the operating lever during counter recoil.
(c) When the gun moves forward back into battery (counter recoil) the lug on the operating lever strikes the operating cam. The lug is forced up and over the operating cam, which rotates the operating lever, which rotates the breech mechanical shaft.
(d) The mechanical lock is broken and the firing pin is retracted in the same manner as manual opening.

Front 5

Extraction and Ejection

Back 5

(a) As the breech nears the fully open position, the extractor cams strike the heels of the extractors, causing them to rotate sharply rearwards.
(b) As the extractors rotate, the lips of the extractors catch the rim of the case base. This breaks the seals between the case base and the chamber. The case base is extracted from the chamber, and ejected from the breechring. As the case base is ejected from the breechring it strikes the bottom of the stub base deflector which guides the case base down into the stub base catcher.
(c) When the SAFE/ARMED lever is left in the safe position the deflector tray rides up and down with the breech.
(d) When the SAFE/ARMED lever is placed in the ARMED position, the deflector tray is locked in the up position once the main gun has returned to battery after firing a round. In this position the stub base deflector guides the stub base of the just fired round down into the stub base catcher.
(e) Once the SAFE/ARMED lever is placed back to SAFE, the deflector tray drops down to the top of the breech block to allow the loader to load another round.