Principles of gas Blowback

I'm a newbie in the sport called airsoft that's why I would also like to share this information to those who's also newbie like me. The purpose of this is to give us some background on how a GGB works.

In airsoft, the highest level of realism is found in gas operated models with blowback (GBB). These are mostly pistols, but there are longer weapons with blowback available as well. Not only is the level
of detailing and weight at a completely different level, but they operate like the real thing as well! But how does it all happen, and can you make it happen even better?

A SHORT HISTORY OF KICK

The first GBB systems can be traced back to Tanio Kobayashi (of Tanio Koba), a grand old man of Japanese model gun and airsoft gun designs, who was working for MGC at the time. The principle was quite simple, having the valve open directly with the pull of the trigger. The blowback system would first propel the slide to the back, and the BB was shot with the exhaust gas. Because of the slide accelerating back, the front of the pistol would "nod" before shooting the BB, causing the BBs to consistently hit low. You also had to pull the trigger decisively to open the valve every time to produce the same amount of blowback. Squeezing slowly would open the valve slowly as well, causing sluggish operation and low fps. Western Arms created the first system that improved lots of things all at once: The hammer was used to open the valve via a firing pin, the BB was shot out before the slide would move, and the blowback system went into hiding in the back of the slide when you racked the
slide manually to get more realistic looks in the ejection port. WA have protected their intellectual property, so other manufacturers can't copy the design without licence. Tanaka Works uses the WA Magna Blowback in their lineup. Mr. Kobayashi continued to develop his system into the "pre-shoot" system which uses a floating valve to direct gas behind the BB before moving the slide, and the nozzle also retracts into the slide when it is moved back. Tanio's design is used by Tokyo Marui in all their pistols now, and many KSC models have a striking resemblance to the principle. For Maruzen, he designed another system that has no moving parts inside the loading nozzle, but the switch valve is located in the top of the magazine.

HOW DOES IT HAPPEN? The magazine of a GBB pistol holds the gas and BBs. The gas is commonly HFC134a (aka. duster gas) or C3H8 (Propane, aka. Green gas, Top gas etc.). Upon firing the trigger, the hammer knocks the main valve open via a firing pin. Another term for the firing pin is "valve knocker". The valve is now open. There are locking devices to keep the valve open for a certain amount of time even when the slide goes back to cock the hammer. Western Arms puts valve locks on their magazines, while others incorporate the lock into the firing mechanism to hold the firing pin (or valve knocker) out. The slide trips the lock later during the cycle to allow the valve to close. The main valve lets the gas into the loading nozzle. Inside the loading nozzle, a switch valve (aka. floating valve, rocket valve...) directs the gas behind the BB to shoot it out of the barrel. The gas flow causes the switch valve to move forward and block the gas flow into the barrel. As the pressure inside the loading nozzle builds up, the slide is forced back by the blowback piston. It has been confirmed with high-speed video equipment, that the BB makes it out of the barrel before the slide has time to move, so the recoil does not affect accuracy! In the WA system, the rear of the loading nozzle is the piston, and the blowback-frame in the rear of the slide wraps around the piston head. In other systems such as Tokyo Marui, the loading nozzle itself is the cylinder, and a piston is fixed to the rear of the slide. In either case, gas pressure is pushing the loading nozzle and slide in the opposite directions. Because the loading nozzle can not move forward, the slide moves back. It's a common misconception that the loading nozzle has to "stick" forward when you rack the slide manually. Don't worry: The pressure holds it forward.

The loading nozzle has a mechanical limit as to how far it can extend, and the slide moves a longer distance than that. After the blowback piston has given the slide all it can, the slide continues to move rearward with inertia, pulling the loading nozzle along. This allows the next BB to move up to the feed lips of the magazine. During the rearward movement, the slide resets the trigger mechanism, cocks the hammer and compresses the recoil spring. The loading nozzle has its own return spring(s) to retract it into the rear of the slide, but the purpose of this is mainly aesthetic. Some models don't have this spring at all, and sometimes a piston head with a tight seal makes the spring unable to retract the nozzle completely. As the slide returns forward pushed by the recoil spring, the loading nozzle picks up a new BB from the magazine and chambers it. The pistol is then ready for another shot.