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The operation of the M61A1 gun is divided into two distinct cycles-the firing cycle and the clearing cycle.

Firing Cycle

The firing cycle begins when power is applied to the firing contact assembly and the gun drive unit simultaneously.

Figure 6-7.-Lubricator assembly installation (F-14). 6-6

Figure 6-8.-Round guided into breech-bolt assembly.

If you look at the rotor from the rear, you see that it revolves in a counterclockwise direction. The ammunition is received from an external source. It is guided into the extractor lip on a breech-bolt assembly by the guide bar fingers (fig. 6-8), The bolt roller shaft follows the main cam path and moves the bolt assembly forward along the rotor tracks, cambering the round.

As the breech-bolt assembly enters the front dwell area of the main cam path, the locking cam forces the bolt shaft down, locking the bolt in the front locking well of the rotor (fig. 6-9). The insulated portion of the contact cam in the firing contact assembly depresses the firing pin cam in the breech-bolt assembly. This moves the firing pin forward against the primer of the round.

Figure 6-9.-Breech-bolt assembly in firing cycle.

The conductor portion of the contact cam makes contact with the firing pin cam, which allows a firing voltage to pass through the firing pin to fire the round.

The breech-bolt assembly remains locked throughout the locking cam period until the projectile leaves the barrel. After the projectile leaves the barrel, the barrel pressure is reduced. The unlocking cam lifts the bolt shaft, retracts the bolt locking block, and unlocks the bolt.

The main cam path guides the breech-bolt assembly rearward The empty case is removed from the chamber by the extractor lip of the bolt assembly. Then, the bolt assembly travels back along the rotor tracks until the guide bar removes the empty case from the bolt extractor lip and ejects it from the gun (fig. 6-10). To complete the cycle, the bolt assembly travels along the rear cam dwell area and into position to receive the next round.

The breech-bolt assembly has now completed a full firing cycle through the elliptical-shaped main cam path.

It has performed seven actions or operations in the following sequence:

1. Feed

2. Chamber

3. Lock

4. Fire

5. Unlock

6. Extract

7. Eject

All six breech-bolt assemblies repeat this firing cycle until the clearing solenoid is actuated, and the gun starts the clearing cycle.

Clearing Cycle

The clearing cycle starts when the clearing solenoid is energized. The clearing solenoid depresses the

Figure 6-10.-Ejection of empty case.

clearing sector arm to the gun housing. This places the clearing sector arm in a ready position. The first bolt assembly that passes the sector arm triggers the actuating pin that lets the sector arm continue to the clearing mode position. This diverts the succeeding bolt assemblies into the clearing cam path (fig. 6-11).

As the breech-bolt assembly picks up a round at the guide bar, the clearing sector arm depresses the bolt roller shaft. This locks the bolt assembly in the rear locking well of the rotor. While locked in this position, the bolt assembly cannot follow the main cam path, so it follows the clearing cam path. The clearing cam path isn't as deep as the main cam path, and it keeps the bolt roller shaft depressed. This firmly locks the bolt assembly in the rear of the rotor body.

The M61A1 gun continues to receive rounds during the clearing cycle. However, because each bolt assembly remains positioned at the back of the rotor during rotation, the guide bar cam fingers eject all unfired rounds. When the clearing solenoid is

Figure 6-11.-Breech-bolt assembly in clearing cycle.

deactivated, the clearing sector arm pivots out of the main cam path. This allows the leaf springs in the rear locking well to force the bolt locking block upward. The bolt roller shaft follows the main cam path that permits the gun to be fired.

If necessary, you may clear the gun manually. To do this, manually pivot the clearing sector cam into the main cam path while turning the rotor by hand.

For further information on the M61A1 automatic gun, you should refer to the M61A1 Automatic Gun, NAVAIR 11-95M61A1-1. NAVAIR 11-95M61A1-1 provides intermediate-level maintenance procedures and includes associated special support equipment.


LEARNING OBJECTIVE: Identify the ammunition handling and gun drive systems of the M61A1 automatic gun. Describe the principles of operation of each system and identify the interrelationship of the various systems.

The ammunition and gun drive subsystems are discussed in the following paragraphs.

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