To send that 6mm plastic death projectile from your weapon to your intended target the weapon needs a power source and there are three types in Airsoft spring, gas and electric.
Spring powered which are commonly referred to as Springers were the first Airsoft guns to come out. These weapons require the user to physically cock the weapon after every shot, not very good and a major disadvantage in an Assault style rifle ! Springers are mainly found as Sniper rifles due to the simplicity of the operation and how quiet they are when being fired, the other style of weapon that uses spring to power it successfully is shotguns some of these can give you a serious workout while using them, no need for that gym membership.
Gas as power source covers three types of propellant which are Green Gas (other colours are available, explanation coming) Co2 and the new old buy is High Pressure Air.
Green Gas -The main component of green gas is pressurized gas, with a mix of silicon oil the gas can be either R144a, R134a or propane. You may see people using gas in White, Green, Red and Black cans these represent different types of green gas which is intended for use in different temperatures and weapon types, but a quick rule of thumb in regards to power output its goes white, green, red then black.
Co2 - Carbon Dioxide with a small amount of oil although these look like the small silver caplets you may see laying in the street that where the similarity ends. You will mainly airsoft Co2 in 12 gram caplets these are a single use once inserted in to the magazine / gun the caplet is pierced and the gas used in small amounts by the weapon until expended.
HPA - High-pressure air (HPA) airsoft guns are actually nothing new. During the early years of what we now call airsoft our airsoft guns were powered similarly to the HPA guns we see today. Though today these guns can be somewhat of a controversial product among the airsoft community, these relatively uncommon airsoft guns can provide a number of key advantages and unique drawbacks as well. To help you understand why airsoft players are so divided about HPA guns, we'll address the question of what is HPA airsoft and take a look at the various pros and cons associated with HPA airsoft guns.
Unlike most gas-powered guns that feature internal gas cartridges or canisters, HPA airsoft guns are powered by an external canister of pressurized air much like most paintball guns. As we previously mentioned, in the past before the advent of the AEG, this was also how many airsoft guns were powered - using external tanks. These large, external canisters provide HPA guns quite a bit more oomph than traditional gas-powered guns, allowing for faster rates of fire and higher FPS. While this may seem to make HPA guns the clear choice for anyone who wants to be as competitive as possible on the airsoft field, there are a number of drawbacks to HPA guns that we will get to later. For now, just understand that an HPA airsoft gun is a gun that is traditionally powered by an external canister of pressurized air as opposed to an internal canister of C02 or green gas.
Electric / AEG - In the realm of airsoft, AEG stands for Automatic electric gun. While other types of airsoft guns use gas or manual pull-back springs to fire projectiles, these battery-powered guns use electricity to drive the firing mechanism. Although the rechargeable batteries make AEGs a less expensive option compared to gas-powered guns, AEG airsoft guns powered by NiMh or LiPo batteries make them very cost-effective compared to gas. This battery powers up a piston inside which propels the BB through a hop up via the inner barrel. The voltage type of the battery will affect its rate of fire.
