After having seen how the gearbox of a Softair replica works, let’s analyze the elements that are located in the upper part of the gearbox and which together form the air group.

The air group

The air group is nothing more than the part of the gearbox that takes care of forfeiting the air inside the barrel; it is probably the most important part of a replica as its good functioning is perceived through the power, trajectory and range of the pellet.

The components that make up the air group (and which we will analyze shortly) are: spring guide, spring, piston, piston head, cylinder, cylinder head and air nozzle.

The syringe test

To understand if the components work well, it is enough to make the famous “test syringe”. In fact, this allows us to identify any air leaks that would compromise correct operation, causing power losses.

To carry out the syringe test, all the components of the air unit must first be extrapolated from the gearbox and then these steps are carried out.

  • Cleans the inside of the cylinder well
  • The cylinder head is inserted in the part furthest from the hole located on the side of the cylinder
  • The cylinder head is closed with a finger so that no air escapes
  • Insert the piston (complete with piston head) into the cylinder with the other hand

Once these steps have been carried out, try to give 2/3 “pumps” to the piston, always keeping the cylinder head clogged.

If the piston remains compressed immediately after the hole positioned on the side of the cylinder, it means that the syringe test has been passed. If instead the piston reaches the end of the cylinderit means that there are air leaks that need to be worked on.

To remedy the leaks, simply insert the various orings into the grooves, lifting them and doing a few rounds of Teflon inside them until you find the right thickness.

The spring

The spring is a fundamental component that determines the power of the replica. Although there are different types on the market, the components to consider are always the usual ones, i.e. hardness and elasticity.

When you buy a spring you will find various abbreviations that vary according to the brand, such as M90, SP90, M100 etc … The numbers after the abbreviation indicate the meters per second with which the dot should come out, but the fact is that there is no model of reference, for this reason an SP90 could be more efficient than an M100 Royal based on the configuration of the air unit of the replica.

Let’s go

Spring guide it is nothing but a pivot of metal or plastic that serves to hold the spring in the usual position, so that it does not get between the gears.

There are various generations of spring guides that correspond to the generation of the gerabox in which it will be installed. They can be shimmed or not and recently there are spring guides on the market that can be adjusted externally to the gearbox to adjust the pressure exerted on the spring.

On the spring guide it is almost always present a cushioned thickness or not which allows the spring to have freedom of movement and above all of rotation on itself.

The cylinder

On the market you can find different types of cylindersuch as those with a hole on the side, without holes, or cylinders with more or less long elliptical holes.

The hole on the side of the cylinder is for making let the air inside of this which will be pushed outwards by the piston. The size of the side hole is useful for deciding which cylinder to mount inside the replica.

Ex: if I have a stubby M4 style replica, I need a cylinder with a long bore and consequently a small compression chamber otherwise I risk that the air will immediately start being pumped into the barrel and the pellet would come out of the replica before the piston reaches the end of its stroke.

The piston

There are many types of pistons which differ according to the teeth, weight and material of construction. The perfect piston cannot be a precise reference model but it will have to be adapted to what everyone wants to get from their replica.

For example, at a high-speed configuration the wear of the piston will certainly be higher because the stops of the piston inside the cylinder will be many more and also the sectorial will engage the teeth of the piston several times.

So for a high speed configuration a light piston is recommended so that it is faster and at the same time very resistant, such as aluminum pistons with aluminum teeth or polycarbonate pistons with steel teeth.

The piston head

It is then connected to the piston the piston head which plays a key role. In fact, the piston head determines, together with the cylinder head, a good air seal as well as greater or lesser noise.


As always, our advice is (especially if you are a beginner) to get the support of an experienced mechanic able to advise you. the best setup for your reply.

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By airsoft