 A manually operated weapon will fire each time the boat is operated and the trigger is squeezed. It's an effective weapon, but its rate of fire is limited. It can fire only as fast as a man can open and close the boat. However, the rate of fire can be greatly increased by using the force of the explosion to operate the boat. When a cartridge is fired, a very high gas pressure is built up inside the case. This pressure pushes the bullet out through the barrel and also pushes in all directions. Three ways have been developed to use this force to operate the boat. The first way is by gas operation. If some of the gas is tapped off to operate the boat, we get a gas operated weapon. By using a model, we'll build up a typical gas operated weapon. When a weapon is fired, the bullet is moved through the barrel by the expanding gas. To tap off some of the gas behind the bullet, we'll drill a hole in the barrel. This hole is called the gas port. Now, when the bullet passes the gas port, some of the gas will escape through the port. To make use of this gas, we'll direct it into a gas cylinder. Inside the gas cylinder, there is a piston which can move back and forth. When the gas from the explosion escapes through the gas port, it strikes this piston and drives it to the rear. To transmit this rearward movement of the piston to the boat, we'll have to connect them. A part like this called an operating rod will do the job. The rod is mounted with one end attached to the piston. It passes through the gas cylinder and the other end is attached to the boat. The operating rod has a slot to unlock the boat. When the piston is forced back by the gas, it moves the operating rod. The operating rod moves back alone a short distance before opening the boat. This gives the bullet time to leave the barrel and when the bolt opens, no dangerous gas will escape to the rear. The rod moves back and the slot cams the lug up and unlocks the boat. As the movement continues, the rod pushes the bolt open. But that is only half the job. The bolt has to be closed again. One way to close it is to use a spring. We've placed the spring between the piston and the back end of the cylinder so that it is compressed with the bolt open. When the spring expands, it forces the piston forward, which pulls the operating rod forward and closes the bolt. Now let's see the whole action when we fire around. Some of the gas escapes into the cylinder, driving the piston to the rear and compressing the spring. At the same time, the bolt is unlocked and then opened. Then the return spring takes over and forces the bolt forward. The force of the explosion has been harnessed so it does all the work of operating the bolt and we have a gas-operated weapon. Gas-operated weapons, such as the BAR or the M1 rifle, can always be identified by a gas cylinder somewhere under the barrel. The second way of using the power of the explosion to operate the bolt is called blowback operation. As the expanding gasses drive the bullet out through the barrel, they also push the cartridge case back hard against the face of the bolt. If this pressure is used to blow the bolt open, we have a blowback-operated weapon. Let's build this type of operation on our model. To permit this blowback pressure to work on the bolt, let's remove the locking lug. Now we'll have to fill up this notch and install a guide lug on the bolt. Now, when the weapon is fired, the bullet moves through the barrel and the bolt begins to open. However, the bullet leaves the barrel before the heavy bolt has opened enough to let any dangerous gas escape to the rear. To close the bolt, a return spring is again the simplest solution. We've attached the spring so that one end is braced against the receiver. The other end pushes against the bolt and when the spring expands, it closes the bolt. Now, let's see what happens when we fire around. The bullet leaves the barrel before the bolt opens. As the bolt opens, the return spring is compressed. Then the spring expands and closes the bolt. Once again, we've used the power of the explosion to do all the work of operating the bolt. But blowback operation is used only with low pressure cartridges because high pressure cartridges would require a very heavy bolt. Weapons of this type, such as the M3 submachine gun, can always be identified by one simple feature. There is no positive locking device on the bolt. The third way of using the gas to operate the bolt is called recoil operation. As you know, most weapons recoil or kick against the shoulder of the man firing. If we use this movement to operate the bolt, we'll have a recoil operated weapon. To harness this recoil and put it to work, the weapon is placed inside a stationary housing known as the receiver. The part originally called the receiver now becomes the barrel extension. The barrel, barrel extension and bolt are locked together and are free to slide in the receiver. Now the trick is to use this rearward movement to unlock and open the bolt. Let's first lengthen the locking lug to make it extend beyond the barrel extension and attach a catch. Now to unlock the bolt, we need some way of pulling this catch down. This cam will do the job. It has a camming slot which fits over this lug on the catch. The cam is fastened to the stationary receiver. Now when a round is fired, recoil sends the barrel, barrel extension and bolt to the rear. At the same time, the catch is cammed down and the bolt is unlocked. The barrel extension strikes the receiver, stops and the bolt continues to the open position. To move the barrel, barrel extension and bolt forward, we'll again use a spring. With the bolt open, the spring is compressed. One end pushes against the bolt. The other end is braced against the receiver. When the spring expands, it first closes the bolt, then pushes the barrel and the barrel extension forward. Let's watch the action again. As the bullet moves out of the barrel, recoil begins. It drives the barrel and barrel extension back and the bolt is unlocked. When the barrel extension is stopped, the bolt continues back. When the bolt is fully opened, the return spring takes over. It first pushes the bolt closed, then the catch slides up the slot and locks the bolt. The return spring continues pushing until the barrel and barrel extension have reached the forward position. Recoil operation is used on such weapons as the pistol and machine guns. If you see the barrel of a weapon moving back and forth inside the receiver during firing, you can be sure it's recoil operated. Remember, there are four types of operation, manual and the three types that use the force of the expanding gas. The gas operated weapon taps off some of the high pressure gas behind the bullet to unlock and open the bolt. The blowback operated weapon uses the rearward force of the explosion to open the bolt and the recoil operated weapon uses the kick caused by the explosion to move the barrel and barrel extension back, unlocking and opening the bolt as it goes. These are the basic principles of types of operation and here we can see how they are used to give plenty of firepower to small arms weapons.