Spring powered
These weapons fire a BB using a simple spring that must be cocked by hand prior to the shot. Most spring weapons are for indoor playing as they have limited range and cycle rates (because they must be hand operated). Typically, spring airsoft weapons are inexpensive compared to similar models in gas or electric format because they do not use any external power to assist in firing the BB. The most inexpensive and readily available of any of these are "springer" pistols, which generally operate by compressing a small piston/spring assembly and simultaneously chambering a BB from the magazine by pulling back the slide every time before firing a shot. Therefore, you cannot shoot fully or semi automatic. Though these guns constitute the vast majority of airsoft guns, there is a large selection of mid-range spring powered rifle replicas on the market, and a handful of high-end precision bolt-action sniper rifles which employ manual cycling in order to drive extremely heavy springs (and hence produce higher muzzle velocities).

Since the airsoft spring pistols are inexpensive, they are suitable for beginners. However, spring guns in the form of rifles are normally not for beginners. A rifle shoots out a more powerful force, sometimes stronger than airsoft electric guns and gas airsoft guns. Some good airsoft sniper rifles also uses spring as the mechanism. The long barrels really boost the speed when firing a shot. Since snipers do not engage in a field combat, airsoft spring guns are suitable as snipers do not need to fire many rounds of shots.

Gas
These weapons fire BBs using green gas. Green gas, also known as common propane, is the more powerful of the two, and is used in most guns with metal slides (upper receivers) In modern gas guns, this is usually a diflourothane or tetraflourthane gas, similar in composition to freon. This is a liquid when inside its container, and remains in that state when injected into the magazine of an airsoft gun. When a valve on the top of the magazine is tripped, some of this liquid is ejected as a gas at high pressure and operates the specific cycling mechanism of the gas gun. Gas guns can typically be grouped into NBB (Non-Blow-Back) and GBB (Gas Blow-Back) categories. NBB guns do not feature a cycling bolt or slide while GBB guns have some sort of moving bolt that realistically chambers a BB from the magazine when cycled. Most NBB and GBB guns come in the form of pistols, with detachable magazines that contain both the BBs and the gas. Some rifles and machine gun replicas are gas operated as well, whether to take advantage of the realism afforded by bolt cycling or to allow adjustable muzzle velocities. The vast majority of all gas guns are produced in Japan and Taiwan. Modern airsoft guns typically can use both HFC134 and the more powerful green gas(propane) and HF22. It is usually recommended that the weaker HFC134 be used with Japanese guns and the stronger HF22 be used with Taiwanese models, for reasons of muzzle velocity limitations and because Taiwanese models are now often equipped with metal slides rather than plastic (which is universal for Japanese guns), meaning that they can take the higher pressure and may not even cycle with lower-pressured gases.

Many older gas guns, now out of production, use CO2 or HPA nitrogen through an external tank and regulator. With the advent of electric guns, this system has become very rare, due to the high cost and instability of gas operation. But the level of quality in construction has prompted many current collectors and players to continue to favour these "classic" airsoft guns.

Recently, players have begun to use propane as a power source, which produces similar results to Green Gas. Chemical composition of green gas has been suspected actually to be either propane or a fluoropropene. Additionally, new gas gun models have appeared that are powered by standard 12 g CO2 capsules, either on a regulated external rig or build into the magazine of the gun itself.

Gas guns generally require more maintenance than an AEG or Spring gun. This is because of all the seals and valves required to hold the gas, and keep the gun from leaking. They need to be lubricated frequently to keep the seals from drying up and cracking. A small solution to this is that Green Gas (HF22) has silicon lubricant in it, therefore it keeps the gun lubricated while using it. Gas guns also have certain weather restrictions, they can be used in just about any weather, however the colder it is outside the less efficiency the gas will provide. Also operating the gun in the cold could cause the valves on the gun and or magazine to freeze and not be able to work until thawed out again. That is typically why gas guns work much better in warmer climates. In the long run, gas guns are also more expensive than buying a spring gun or AEG because you must continually buy more gas to power it, and lubricant to keep it working well. As opposed to AEG's which only require lubricant, and a battery which can be recharged many times.

Automatic Electric Guns
Also known as AEGs These weapons are powered by batteries and an electric motor, which cycles an internal piston/spring assembly in order to launch the BB projectile. These are by far the most common Airsoft weapons in "serious" competition use today. These guns were originally developed in Japan, and the Japanese model giant Tokyo Marui dominates the market today with many quality models. In a Marui AEG, the motor drives a series of 3 gears mounted inside a gearbox. The gears then compress a piston assemble against a spring. Once the piston is released, the spring drives it forward through the cylinder to push a BB into the chamber, through the barrel, and forward from the muzzle. Many manufacturers have now more or less replicated this basic model, adding reinforced parts or minor improvements. But it remains the general design common to almost all modern AEGs (with the exception of the TOP machine gun line).

In recent years, challengers to Tokyo Marui from Taiwan and Hong Kong have begun producing AEGs as well, emphasizing primarily on inexpensive metal parts. Classic Army of Hong Kong and ICS of Taiwan, who both have had long experience producing aftermarket accessories and reinforced parts for Marui AEGs, first began with versions of the Heckler and Koch MP5, a model which Marui had produced for some time. Both versions boasted metal receivers and parts, with essentially the same internal design as their Marui predecessor. And both initially suffered from quality control issues which marred their brand name for several product generations. Currently, both companies have begun to branch out in different directions from Tokyo Marui. The ICS M4/CAR-97 carbine features an innovative swing-open gearbox and receiver and an anti-reversal latch disengage built into the forward assist button. The Classic Army CA33E replica of the HK33E is a rifle model which Marui does not produce at all. Quality control has appeared to have improved as well on current models for both brands.

Electric motors generations:

EG560 1st Generation Tokyo Marui Motor. No longer used, except for a specially tuned version in the FAMAS.
EG700 2nd Generation Tokyo Marui Motor. Standard in most guns.
EG1000 3rd Generation Tokyo Marui Motor. Higher speed motor than the EG700 motor, but with slightly less torque. Widely accepted as the best stock motor.

Gun parts and upgrades
After a while most players begin to think about upgrades and to improve their weapon. The first thought is probably to increase the muzzle velocity to gain extra range. But the only weapons that need longer ranges are rifles such as sniper rifles and the real normal intention is to increase the durability and lifespan of the weapon. Most players settle for merely increasing the battery size and spring strength. When an airsoft weapon is upgraded to increase muzzle velocity, the weapons lifespan will decrease. The power of an airsoft weapon depends on three things: the strength of the spring that pushes the piston forward, the amount of air the piston compresses and the precision of the barrel. When a weapon is highly upgraded it becomes a specialised tool for serious airsoft skirmish and to dryfire (i.e. without bullets) puts an increased strain on the parts.

Always remember that upgrades can invalidate warranty.

Spring
There is two ways to measure how strong a spring is compared to a standard spring. The Percentage system and the Meter Per Second system. A standard AEG has a muzzle velocity of 90 m/s (100%) with a 0.20 g bullet. A M100 spring increases this velocity to 100 m/s. There are M100, M120, M130, M140, M150 and M160 springs. The percentage system is harder to use since it doesn't easily tell what the weapon will perform like. A very powerful spring requires that the entire gearbox is replaced.

Bearings & bushings
The axles inside the gearbox are attached to the housing by small plastic bearings and these will eventually wear down. If these bearings are exchanged to metal bushings or even ball bearings, the lifespan of the mechbox will increase (almost double according to many players). Ball bearings allow higher rates of fire as well. Shims are thin metal washers added to the axles that make sure that the gears in the gearbox are precisely aligned.

Barrel
A standard airsoft barrel often has an internal diameter of 6.12 mm. If this barrel is exchanged for a precision barrel with a 6.04 mm internal diameter the amount of air that slips by the bullet reduces and the benefits is that the bullet has less spread and about 5% extra velocity. The downside is that the barrel clogs up more often and has to be cleaned. A longer barrel increase range, but the barrel can't be too long since if the amount of air in the barrel is more than the amount of air the piston push forward, a vacuum will develop in the barrel and the bullet will be sucked back with a big speed reduction. There is a method called "cratercutting" that has the effect that just before the bullet leaves the barrel the air slips by and cuts a hole in the wall of air that is formed in front of the barrel. This technique is normally used by players aiming to increase the range of the weapon.

Battery
If a battery's voltage increases, so do the rounds per minute in an AEG motor. All standard AEG batteries have a voltage of 8.4 volts and the only difference between the different sizes is that a large battery has a capacity of 1300 mAh, while the other small standard batteries have capacity of 600 mAh. This means that a large battery will last for about twice the amount of shots. Upgrades inside a gearbox often reduce the rate of fire and if you then use a battery with a higher voltage like 9.6 V or 10.8 V the rate of fire wont drop as much or even increase. A higher voltage also wears a motor down faster and more maintenance is required. It is possible to use 12 V to power an AEG but this isn't to recommend since the wear is increase very much, the contacts in the trigger is faster worn out and the overall lifespan is sharply reduced.

A battery with a higher capacity (more mAh), will last longer on the field. An upgraded weapon also requires more current and the amount of shots that can be fired will decrease unless a bigger battery (more mah)is used. The usual battery is NiCd (Nickel Cadmium), but there is another type called NiMH (Nickel Metal Hydryde). The NiMH usually has a higher capacity (mAh), but usually offer less AMPs and can't drive the larger springs (ie M120). However if you do your research you will find "high drain" NIMH batteries available as well. A 20 amp or higher "drain" is ample for most upgrades on an AEG. A 30 amp will drive even the highest powered springs (m130+)

Gears
The normal gears in a gearbox have an approximate lifespan of 30,000 shots, and a new set of gears will last longer since they are made from a material of greater strength. There is a set that increase rate of fire and reduce the motors power or reduce rate of fire but increase the motors power. The "Helical Cut Gears" is special gears that has a better grip between the gears and doesn't brake as easy as standard gears. The largest supplier of upgrade and replacement parts is Systema.

Nozzle
It is a small plastic or metal nozzle that seals the space between the air-piston and the BB pellet. This upgrade helps to maximise the air-flow fed from the cylinder to the barrel, therefore reducing wasted air pressure and resulting in a slightly increased muzzle velocity.

Motor
Most upgrades reduce the rate of fire. By switching to a stronger motor the rate of fire isn't reduced as much. An upgraded AEG should have at least an EG700 motor. The strongest motor is EG1000. All new models that Tokyo Marui releases have EG1000 motors, but many of the older models have EG700 or even EG560. Not all AEG can have a motor upgrade. If the spring isn't replaced with a stronger than M120 the EG560 motor can take it, but the battery will probably has to be changed to a 9,6 V or even 10.8 V.

Piston
With stronger springs and tighter barrels, the physical strain on your piston and cylinder head increases. A piston can be equipped with a "silent" or "anti-vacuum" piston head. The silent piston head reduce the impact the piston makes in the cylinder and also reduce noise. The Anti Vacuum piston head prevents the forming of vacuum in the cylinder, this means that the barrel length can be extended without too much risk of the "dreaded suck".

Mechbox
This is a totally new mechbox with new and better gears, stronger spring, nozzle and other improvements (see below). This isn't a cheap upgrade but the durability and lifespan increase and so do the muzzle velocity and overall performance. A new mechbox isn't available to all models, like the FAMAS doesn't have an upgraded mechbox. There are different versions of mechboxes since they're used in different weapon models.