Benefits of Having MOSFET in an Airsoft Gun

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Ok, so you got your basic gear: a new replica, brand new set of magazines, face and eye protection, magazine pouches and rest of your loadout. But your new weapon lacks a little something in battle, the trigger response is slow, RPS is just meh. Once your milsim veteran friend told you about upgrading to a MOSFET unit, and how it could solve such problems and generally enhances your weapon.

Now, are you thinking about modding your weapon with a dedicated MOSFET unit? Still, considering if it is worth the effort? This article will explain why and when it is a good idea to optimize your gear. 

The basic theory is simple: every Automatic Electric Gun (AEG) needs a battery, from which the energy is used to power an electric motor.  This motor is enclosed inside the AEG’s grip. For a basic configuration (AEG without MOSFET unit), AEG’s wiring looks like this:

To shoot, you need to pull the trigger. By doing so, you are closing the circuit, allowing the current to flow from the battery through to the motor. This is simple but has some drawbacks: 

  1. First of all, the trigger’s metal contacts are not ideal and have unwanted resistance. This resistance makes your weapon shoot slower (lower Rounds Per Second) because it limits the maximum electric current flowing through your motor. 
  2. Unfortunately, current that flows here is pretty high – in the magnitude of tens of Amperes. Each time you shoot, a high voltage spike created by the motor may cause an electric arc. This arc will melt and erode trigger’s contacts, damaging them over time.
  3. Damaged and worn contacts have more electrical resistance. This is why occasionally you have to clean or even replace the trigger’s contacts set. Otherwise, your airsoft gun will shoot slower, or stop shooting completely. And that’s not something any airsoft player would like to experience.
  4. Electrical contacts with standard wiring are not waterproof – when a large current flows through a wet contact it erodes the trigger pack even more than normal.

Table of contents

  1. What is a MOSFET unit?
  2. Benefits of using a MOSFET unit
  3. Drawbacks of using MOSFET unit
  4. Is it hard to install an Airsoft MOSFET?
  5. Advanced MOSFET features
  6. Summary

What is a MOSFET unit?

MOSFET is an electronic switch, that will close the circuit electronically. It is a way more efficient power delivery system for your AEG, much better than a traditional, metal contact switch. Layman’s terms a MOSFET is protection for your weapon trigger.

The trigger switch is still used to activate the flow of electricity, but it only activates the MOSFET itself. If you pull the trigger, the MOSFET will start to conduct electricity, and high current will flow from the battery, through the MOSFET unit (but not directly through the contacts pack) to the motor. This prevents wear and tear of the trigger switch assembly

If you would like to dive deeper into this topic – make sure you check this article.

Benefits of using a MOSFET unit

What are the main benefits over just using metal contacts? 

  • Using a MOSFET has much lower resistance, allowing for more electricity to flow to the motor. This results in an increased rate of fire (ROF) and a faster trigger response
  • A small current flows through trigger contacts (just to activate the MOSFET), so there is no risk of damaging them,
  • No need for the tedious and time-consuming disassembly of the gearbox only to clean trigger contacts.
  • Airsoft MOSFETs that come with a microcontroller onboard give way more features than you can think of. Features, such as ActiveBrake, battery diagnostics, electronics fuse or customizable fire modes which will be explained in the last section.

Drawbacks of using MOSFET unit

  • Be careful when using DIY or low-quality airsoft MOSFET units, you may save a few bucks, but you risk damaging your airsoft gun. Because the motor has high power and has an inductive load, without the proper protection, a MOSFET can be damaged and can cause a short circuit. In the best-case scenario, you will only smell burnt electronics, in the worst case, your replica could catch on fire. High-quality factory-made MOSFETs are waterproof and this is a nice thing to have, manufacturers call this feature “tactical waterproofing”, “water protection ” or “military-grade electronics coat” just have it in mind that any protection is better than none

Check the MOSFET dedicated to electronic pistols made by Smart Armaments

  • Using a discharged battery can destroy your MOSFET unit. This is related to the MOSFET switching its ON/OFF phase. You should always read the product datasheet, as the manufacturer of yours MOSFET will specify the required battery voltage operating range.
  • MOSFET unit installation will require the rewiring of your AEG cables. If doing it by yourself, you have to be careful. Too long, too short or too big wires and you will not be able to reassemble your replica. Too small wires and you will lose RPS (Rounds per Second) and they can overheat due to the high current flow.
  • MOSFET unit and installation can be expensive. A basic airsoft MOSFET costs around $30. More featured units, such as an active brake MOSFET may cost around $50. And even more sophisticated units, such as microprocessor-controlled units can range from $70 to $100. The installation (including disassembly and reassembly of the entire AEG) can take anywhere between 2 and 4 hours.

Is it worth to buy cheap MOSFETs? We discussed this topic in another article which you can access by clicking here.

Is it hard to install an Airsoft MOSFET?

Installing an airsoft MOSFET by yourself can save you money. If you are inexperienced at soldering, the whole process may take you up to a few hours. In order to do it by yourself, make sure you have at least:

  • soldering iron,
  • solder wire and some flux
  • low-resistance wires,
  • MOSFET unit or kit,
  • pliers, side cutters,
  • heat shrink tubes,
  • multimeter

The more advanced the MOSFET unit is, the longer the installation process can take. Note that buying a commercial product kit gives you all the necessary parts (excluding tools) and quite often you can get a “complete kit” or “drop-in set” that contains all connectors and parts already soldered so you do not have to use a soldering iron

If you need more information about the process you can check our guide to installing an airsoft MOSFET to an AEG or an AEP.

Advanced MOSFET features:

  • ActiveBrake – This function allows the MOSFET unit to use the motor as a brake. This will allow for compensating gearbox overshots when using high RPS tuned gearbox. Please be aware that this puts a strain on your gearbox and motor. As a result, it may cause premature failures. 
  • Battery diagnostics & protection – some airsoft MOSFETs have built-in battery under-voltage protection. It either warns you when the battery voltage is getting low or turns off your replica. This is very useful for li-po/li-ion batteries, as it extends the lifetime.
  • Customizable fire modes – Safe-Semi-Burst, Safe-Semi-Semi. You can configure your airsoft gun in such a way, that auto mode will become so-called burst mode, and your AEG will shoot 3 bullets per one trigger pull. Other modes allow you e.g. to turn off automatic fire mode completely if, for example, your playing field, milsim, scenarios or other rules require that.
  • Electronic fuse – microcontroller will stop shooting when a high current drain is detected (like a short circuit), or when the MOSFET temperature gets too high. This is to prevent the AEG from getting damaged.


If you have the right tools, a MOSFET unit may need up to 4 hours for installation, and a budget of around $70 for a simple unit. However, the range of additional features is wide. Starting from the safety improvements to your airsoft gun to advanced fire modes like burst fire or spring precocking. In my personal opinion – it is totally worth the price and time needed to install it.

But what, when you would like to extend your airsoft pistol (aka AEP) with all the advantages of a MOSFET? You should totally check out the dedicated SIGMA AEP MOSFET.

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