Specna Arms M90 Main Spring

The Specna Arms M90 Main Spring is an AEG main spring that determines the energy transfer within the gearbox and ensures a consistent, lower FPS output. Thanks to its even spring tension and stable compression, the gearbox continues to cycle smoothly, ensuring your replica performs predictably during maintenance, refurbishment or a carefully tuned CQB build.

With an AEG, a great deal of attention is paid to components such as gears, the hop-up mechanism and the motor, whilst the main spring ultimately determines how much energy is available for each shot. As soon as a spring becomes fatigued or loses tension, fluctuations in FPS often occur and the feel of the gearbox also changes. A new M90 main spring restores that balance and ensures that all internal components work together again as intended.

An M90 spring is particularly useful if you want to adjust a replica to a lower field limit or rebuild an existing gearbox. When combined with a well-shimmed gearbox, a proper air seal and high-quality internal parts, this produces a much more consistent result than simply replacing a single worn part.

When do you actually notice a difference?

You’ll notice the biggest difference if your replica previously produced inconsistent chronograph results or started to fire less smoothly. A consistent spring tension ensures that the piston is subjected to virtually the same load with every cycle. This translates into more stable FPS readings and a predictable shot pattern, something that is particularly noticeable during CQB or technical training sessions.

During overhauls, we regularly see players investing in new gears or a powerful motor, whilst simply reusing the old main spring. It is precisely this combination that can lead to unnecessary strain, an erratic gearbox cycle or unexpected FPS fluctuations. Replacing the main spring often prevents these kinds of problems at an early stage.

Why do experienced players choose a Specna Arms M90 Main Spring?

Specna Arms uses high-quality spring steel with polished ends, allowing the spring to move smoothly against the spring guide and piston. This reduces friction during compression and prevents unnecessary wear on contact surfaces inside the gearbox.

In addition, this main spring features an irregular coil pattern. This design helps to minimise what is known as ‘spring flutter’ during the cycle. As a result, the spring operates more stably and retains its properties for longer than simple springs with a standard coil pattern.

An additional benefit that is often underestimated is that a consistent main spring also makes it easier to adjust your hop-up. When the muzzle velocity fluctuates less, the BB reacts more predictably to the same hop-up setting.

Which setup is this main spring suitable for?

The Specna Arms M90 Main Spring is best suited to replicas designed for CQB, indoor airsoft or training purposes where a lower energy output is required. This spring is also a logical choice for servicing a V2 or V3 gearbox when the original spring has become worn out.

Combine this upgrade with a new piston, piston head, nozzle, cylinder and high-quality gears to ensure the entire powertrain is optimally matched once again. You should also always check the gearbox’s air seal; even the best main spring cannot compensate for inconsistent performance if there is an air leak.

Practical insights that many players overlook

A common mistake is to replace only the motor or gearset when the replica starts to fire less consistently. In reality, the cause often turns out to be a main spring that has lost some of its tension.

It is also often thought that a higher FPS automatically results in better performance. In practice, a stable power output and consistent shots almost always ensure better accuracy than a replica whose FPS varies significantly.

Finally, it is advisable to carry out another chronograph test after assembly. Minor differences in the airseal, cylinder capacity or piston weight can mean that the same M90 spring produces slightly different muzzle velocities in two identical replicas.

Key features

• M90 spring strength ensures a controlled reduction in FPS output, making it easier for the replica to remain within CQB or field limits.
• High-quality spring steel retains its tension over the long term, meaning that performance does not deteriorate as quickly after intensive use.
• Irregular coiling reduces spring vibrations during the gearbox cycle, resulting in smoother firing behaviour.
• Polished ends reduce friction on the spring guide and piston, ensuring that the internal components are subjected to a more even load.

Who is this main spring suitable for?

This main spring is a good choice for players who are refurbishing an AEG, want to adjust a replica to a lower FPS, or are looking for maximum consistency during CQB and technical builds.

If you use your replica solely for recreational purposes and the current FPS readings are still stable, replacement is not immediately necessary. However, if you are rebuilding a gearbox or wish to achieve consistent chronograph results, a high-quality main spring clearly offers added value.

Frequently Asked Questions

Is an M90 main spring suitable for every AEG?
Most V2 and V3 gearboxes can use an M90 spring, but the final FPS also depends on the cylinder capacity, airseal, barrel length and other internal components.

What FPS does an M90 main spring deliver?
That varies from replica to replica. Factors such as compression, barrel length and gearbox efficiency have a major influence on the final muzzle velocity.

When should I replace my main spring?
If you notice that the FPS is steadily dropping, chronograph results are fluctuating significantly, or your gearbox is being overhauled, it is advisable to replace the main spring at the same time.

Will a new main spring affect the service life of my gearbox?
A correctly selected main spring balances the load more effectively. As a result, the internal components are subjected to a more even load than when a worn or incorrect spring is used.

Which parts should I combine this upgrade with?
For the best results, combine this main spring with a good spring guide, piston, piston head, nozzle, cylinder and high-quality gears, and check the gearbox’s air seal thoroughly straight away.

Would you like to restore your AEG to a stable power output and predictable performance? Then the Specna Arms M90 Main Spring is the obvious choice for a reliable and precisely tuned gearbox.