HPA - An abbreviation for "high pressure air", this gas is used for custom airsoft guns that will probably never be seen in a given game. Modified Classic Airsoft guns may use this gas, but many people do not use it for a few reasons: the tanks are expensive, while the refills are inexpensive but require pressure regulation.
HFC 134a – Designed for Japanese pistols, it generally has a low velocity and low pressure with a decent FPS for skirmishing. Also known as white gas, this gas is mainly used in non-modified guns made by Western Arms, Tokyo Marui, Marushin, Maruzen, and some KSC guns.
Green/Top Gas – It is probably the most-used gas in airsoft, but only safe to use on Taiwanese and full metal guns when considering the pressure it provides on the internals of a gun. Composed of propane, silicone, and other elements, this gas should not be used for any propane purposes; i.e. this gas is strictly to be used for airsoft. Japanese guns are NOT made for the pressure of green gas unless its internals have been upgraded fully. If green gas are used on these guns, they lose integrity and break.
Red Gas – A very powerful gas that is designed for full metal guns only (this includes full metal Taiwanese guns, heavily modified Japanese guns, Taiwanese gas rifles, modified Japanese gas rifles). Unfortunately, this gas (also known as methane) wears out the gun much faster. If a gun was "made" to take red gas, this does not necessarily mean that the internals are reinforced to taking the constant build-up pressure of the red gas. The rubber O-rings (any seals in general) and other small, frail plastic parts are all subject to the high pressures of red gas, which results in more tension and stress on these parts. Mistaken by some, red gas is NOT CO2. It is best to not use red gas at all unless the gun has been advertised to take red gas.
CO2 – This may be known as black gas, where it is stronger than all of the other gases, with a much higher pressure and can create very high FPS gain. But it has the downside that the FPS may go further than legal limit. CO2 expands at a higher rate than green gas; therefore it will shoot harder, but will freeze faster during rapid fire. The pressure that it places onto the seals can lead for the seals to need to be replaced after a certain amount of firing. This gun can be used on several WE Hi Capas, the AE Homeland Defender, and Classic Airsoft guns.
N2 - Known as nitrogen, this gas is seen often in paintball games with the possible name of N2/HPA (High-Pressure Air). The tanks are typically a little bigger than paintball tanks and if they are in use then they ALWAYS have a regulator attached to them. This gas system is use in higher-end paintball guns instead of CO2 because it is more consistent over various air-pressures and temperatures extremes. Unfortunately for airsoft guns, the power source and regulation system for this stuff is difficult to deal with: the typical output pressure on the tanks, even with regulated is in the 850PSI range. Most CO2 powered airsoft guns will probably take N2/HPA with a preset regulated N2 tank and certain high end systems, but at a hefty price.
A few small notes:
- Don't mix gases: it's rather pointless. The difference in pressures and fps are small. Except for low-powered WA guns, there is very little difference in any other gun when mixing gases.
- For non-blowback guns, the gas that it can use will mainly depend on the gun. If it is a cheap gun, then, no matter what gas is being used, the gun will break.
- Stay away from the non-blowback guns that have plastic mags. These have been noted to leak out of the box
- When it comes to dry firing, if it is done a lot, it will wear/break springs faster in your gun. You can keep a small amount of pressure inside of the magazines for storage, but never have too much if you are storing them. A small amount of gas in the magazines during storage will help preserve the O-rings. (Replacing O-rings isn't hard, but is tedious to find the correct size. When replacing O-rings, make sure they are fully lubricated with silicone oil.) Remember, airsoft guns were not made to dry fire, so keep it to a minimum.
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