Half-loading is a term associated with the .50-caliber BMG. It can be compared to feeding. Feeding is the first of eight steps in a cycle of operation. It places a round in the receiver just to the rear of the receiver. Do not confuse loading the .50-caliber BMG (described earlier) with half-loading. The two operations are different.

Half-loading the gun is done after the ammunition belt is installed and the cover group closed. To half-load the gun, the gunner grasps the retracting slide handle, pulls it smartly to the rear, and releases it. At this point, two things can occur. What happens depends on whether the gun is set for automatic or semiautomatic fire.

Figure 13-47.-Feeding mechanism parts of the receiver setup for left-hand and right-hand feeding.

When the gun is set for automatic free, the bolt latch release lock holds the bolt latch release down. When the retracting slide handle is released, it and the bolt will go forward. They are driven forward under pressure from the driving spring group. The gun is now half-loaded (in automatic).

When the gun is set for semiautomatic fire, the bolt latch release is up. When the retracting slide handle is released, it and the bolt will remain to the rear. To complete the half-load operation, the gunner must do two things. First, the retracting slide handle must be pushed all the way forward. Second, the bolt latch release must be depressed. That unlocks the bolt and it drives forward. The gun is now half-loaded (in semiautomatic).

Can the .50-caliber BMG be fired now that it is half-loaded? The answer is no. Half-loading only places a round into the receiver behind the barrel. The round must be chambered before it can be fired.

Full-Loading Operation

Full-1oading a .50-caliber BMG can be compared to cambering. Cambering was the second of eight steps in a cycle of operation. It places a new round in the chamber of the gun.

To load the gun fully, you must repeat the half-loading sequence. Pull the retracting slide handle to the rear and release it. The weapon is now ready to fire.

Unloading Operation

To unload a .50-caliber BMG, unlock the bolt release latch (if applicable) and open the cover group. Lift the ammunition belt out of the feedway. Pull the retracting slide handle to the rear and lock the bolt. Look and/or feel to make sure no ammunition is in the gun.

If the weapon is clear, lower the extractor. Release the bolt and ease the retracting slide handle forward. Then lower and secure the cover group. To complete unloading operations, depress the trigger to uncock the firing mechanism.

Cycle of Operation

The first two steps of the eight-step cycle of operation have already been discussed. Initial feeding and cambering are accomplished during the manual half- and full-loading operations. After the first round is fired, feeding and cambering are done by the action of the gun.

The remaining steps in the cycle of operation of a .50-caliber BMG are summarized below.

1. Locking-The bolt is locked to the barrel and barrel extension.

2. Firing-The firing pin is released and driven forward to strike the primer of the cartridge.

3. Unlocking-The bolt unlocks from the barrel and barrel extension.

4. Extracting-The empty cartridge case is pulled from the chamber.

5. Ejecting-the empty cartridge case is ejected from the receiver.

6. Cocking-The firing pin is withdrawn into its cocked position.

Figure 13-48.-The .50-caliber BMG receiver; cutaway view.

You can follow most of the operating cycle of the gun by referring to figure 13-48. Assume the chamber is loaded, the gun is cocked, and the bolt latch is released. When the trigger is depressed, the trigger bar pivots and releases the cocked firing mechanism. The spring-loaded firing pin strikes the primer and the cartridge fires. Pressure from the expanding gases causes the recoiling parts of the gun to start moving rearward.

During the first 3/4 inch of rearward travel, the recoiling parts remain locked together. However, the breech lock depressors are acting on the breech lock pin. That action forces the breech lock down and out of the bolt. As a result, at the end of the first 3/4 inch of recoil, the bolt is unlocked. It is free to continue recoiling independent of the barrel and barrel extension. The barrel extension hits the accelerator. It, in turn, hits the bolt and accelerates it (the bolt) to the rear. The barrel and barrel extension recoil another 3/8 inch (1 l/8-inch-total travel). They are stopped by the buffer assembly.

Meanwhile, the bolt recoils an additional 6 3/8 inches to the rear (7 1/8-inch-total travel). During this movement, the driving spring group is compressed and the bolt is stopped by the bolt buffer mechanism. The fired cartridge is extracted and the firing mechanism is cocked.

Counter recoil forces the-bolt forward and the empty cartridge case is ejected. The bolt locks to the barrel extension and both move forward into the battery. Feeding and cambering have taken place and the gun is ready to fire. The cycle begins when the firing pin is released to set off the next cartridge.