The piston in your AEG translates the rotational movement of your gears into linear movement of the piston. This piston (when paired with a piston head) compresses the air in the cylinder and propels your airsoft ammunition down range.

You may be looking to replace your AEG’s piston for a repair, upgrades or just to learn and this FAQ should answer any questions that you may have about choosing the right AEG piston for you.If you need more answers, contact us on facebooktwittertelephone or email info@majorairsoft.co.uk and we’ll help you out (and update the FAQ!).

What piston is best?

As with anything in airsoft, there is no ‘best’ piston and it all depends on what you want from your AEG. You should carefully consider the pros and cons of each aspect of your piston such as body material, teeth material, how many metal teeth and the weight of the piston. The negatives and benefits of each shall be highlighted in the questions below.

How many teeth should my piston have and will any piston work?

No, not all piston’s will work in all guns. Whilst the majority of AEG pistons will work in the majority of AEGs, there are a few special types that may catch you off-guard and out of pocket.

V2, V3 and V7 gearboxes all use interchangeable pistons. These pistons have a standard diameter and 15 teeth. (Some of our pistons are labelled as having 14 teeth, this is because one has been removed to allow easier correction of Angle of Engagement. They are still compatible.)

V2 extended or V2.5 gearboxes (often used in an SR25), use a piston that is longer than the standard 15 teeth. The V2.5 AEG gearbox requires a piston of 19 teeth long which allows the piston to travel further and compress more air. Ensure that you are purchasing a piston with 19 (or 18) teeth for it to be compatible with this type of gun.

Pistons labelled with a ‘half-rack’ have one side of all their teeth removed. These pistons *may* work in AEGs with the same number of teeth, but it cannot be guaranteed. Half Rack pistons are designed to give clearance to helical gear sets that can be known to rub or snag on standard pistons.

Do I want a metal or plastic piston?

A metal airsoft piston will inevitably be stronger than any plastic counterpart. Its metal construction will be able to withstand the strain and shock that happens within an AEG with ease. However, it comes with downsides. Metal pistons are generally heavier than plastic pistons and this can lead to a marginally slower rate of fire and trigger response, as well as add to the noise that you gun makes when firing.

Plastic pistons are much cheaper, lighter and weaker than metal pistons. They are often used within high rate of fire weapons. The low weight of these pistons means that they produce less noise and vibration when firing.

Plastic pistons are often used as a redundancy within a gearbox, or a first point of failure. This is due to how cheap they are to replace. It’s much cheaper to replace a plastic piston than it is to replace a metal one that has broken and destroyed other parts in the gearbox with its metal shards.

How many metal teeth should my piston have?

This completely depends on the stress of your gearbox build. A high rate of fire or high FPS AEG should have more metal teeth, due to increased wear. It is often a good idea to use a full plastic piston until you are happy with how smooth your AEG is running. In the event of a malfunction in your gearbox (due to incorrect AOE, pre-engagement, etc), your piston will break and send parts of it into the gears. If your piston and piston teeth are made of plastic, it will limit the damage done to your gears and other parts, unlike metal teeth.When your AEG can run with a plastic piston in a high stress build without breaking (other than normal wear), your RIF/IF is tuned to a point where it’s smart to put in a metal toothed piston.

Will a new piston improve my Rate of Fire / Trigger Response?

It may improve your rate of fire and trigger response. It may also make it slower.The new piston would need to be lighter than your current piston in order to improve rate of fire or trigger response. Even then, it would only do so marginally.

Why do some pistons have one tooth less?

The majority of airsoft pistons have 15 teeth (see above), but some pistons have 14 teeth. This is because the 2 pick-up tooth has been removed to make it easier for you to correct the AOE of your airsoft gun and improve it reliability.

What is AOE?

AOE (Angle Of Engagement) is the angle in which the sector gear engages with the piston teeth. If this angle is incorrect (as it often is from the factory), it will put unnecessary stress on the piston and gears, eventually causing it to fail.The sector gear should engage with the piston at the flattest angle possible, so that they teeth contact with the most surface area.In some instances, another tooth may get in the way before you can get that optimal angle, this is where a file or a 14 tooth piston is recommended.

What is Swiss Cheese?

Swiss cheese is cheese with holes in it (stay with me). A swiss cheese piston is a piston that has holes in it. As outlined above, a lighter piston often results in a slightly faster FPS, so people often drill holes in their airsoft pistons in order to get a better RPS (rounds per second). This does not make your piston edible.

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As always, if you have any questions that are left unanswered after this airsoft piston FAQ, please contact us at info@majorairsoft.co.uk and we’ll be more than happy to help!