Actions: Gas Operated: Recap

Let us now recap what we've learned about gas operated systems in the last few posts:

1. Gas operated systems work by utilizing some of the high-pressure gas generated by firing a cartridge, to operate their extraction, reloading and cocking mechanisms.
2. These are generally used for weapons like rifles and shotguns. For example, most modern self-loading and assault rifles designed during and after World War II use gas operation. Examples include: AK-47 and its descendants, FN FAL, M16 family, M1 rifle and carbine, Valmet, Galil etc.
3. The two main ways of using a gas operated system is to (a) make the gas act upon a piston, which drives the rest of the system or (b) make the gas directly impinge upon the bolt and bolt carrier.
4. Main problem with gas operated systems is that the gas tends to leave corrosive deposits on the working parts. Different gas operated systems handle this issue in different ways.
5. Another problem with gas operated systems is that the heat from the gas causes metal parts to expand. Due to unequal expansion rates of the various components, they must be well lubricated to prevent excess wear and tear.
6. Because of the weight of the parts moving after the weapon is fired, gas operated systems using pistons lose some accuracy because of the vibrations and shift in balance. This especially significant in the case of automatic firing weapons. This problem is reduced with direct impingement systems because the mass of moving parts is lesser than a piston driven system.
7. On the other hand, piston driven systems are generally more reliable because the gas only acts on the piston and is not allowed to directly act upon the rest of the mechanism. Direct impingement systems need to be cleaned and maintained more regularly because the gas acts upon much of the mechanism.

As we mentioned above, the hot high pressure gases generated by an exploding cartridge often carry corrosive chemicals with them. Upon cooling, these chemicals deposit upon the operating parts of the action. If the build up is too much, this will lead to jamming and reliability issues. All gas operated systems must therefore have some way to deal with this situation. For example, in piston driven systems, the gas is only allowed to act on a piston, thereby protecting the rest of the parts from heat and corrosion. Additionally, on an AK-47, the piston has sharp edges on its face, which in theory, scrape the built-up deposits from the walls of the cylinder. These scrapings get vented out the next time the weapon fires. In direct impingement systems such as the M-16, some parts such as the gas tube are somewhat self-cleaning and not designed to be user-serviced in the field. Other parts, such as the bolt and carrier are designed for easy access, so that they can be properly cleaned.

Most modern assault rifles and squad automatic weapons (SAW) in use today utilize the gas operated action principle. This shows the popularity and success of this type of mechanism.