Frequently Asked Questions

You’re interested in getting into HPA but don’t know where to start? Here you will find the answers to the most commonly asked questions regarding our systems and HPA in general to help you get started in the world of HPA airsoft. This section will be updated regularly based on feedback from customers like you so, if you don’t see the answer to your question, please email us at and we will be happy to help.

HPA 101

We currently offer three different lines of HPA conversion systems. There is the Fusion Engine which is a complete drop-in replacement for an AEG's gearbox. So, you just remove the whole gearbox and drop the Fusion Engine into the rifle in its place. Then we also have the F1 and JACK HPA conversion kits which are cylinder replacement systems for an AEG's gearbox. These reuse the original gearbox shell and simply replace the gearbox's internal components.

No, our systems are designed to work with the AEG's original barrel, hop-up and magazines so nothing needs to be changed.

Three different components are needed to run our systems. You will need a regulated air rig capable of regulating output pressure to 120psi and below, a HPA (High Pressure Air) tank and a battery to power the on board FCU (Fire Control Unit).

All of our systems require minimal maintenance as each system only has at most 2 moving parts. We recommend disassembling, cleaning and greasing each system after every 30,000 to 50,000 shots.

The PolarStar HPA conversions can be separated into two broad categories: Dual Solenoid (Fusion Engine) and Single Solenoid (JACK and F1) systems. Dual solenoid systems use two solenoids to move the nozzle and fire the round. This allows each action to be controlled separately and precisely. Single solenoid systems have only one solenoid, which controls nozzle movement from it's retracted idle position to the forward firing position. The firing air is not directly controlled by the solenoid, but by the position of the nozzle as it moves forward to chamber the round.

JACK uses a small solenoid for nozzle movement only. The position of the nozzle within JACK is what allows or prevents air from flowing down the nozzle.

Like JACK, the solenoid in F1 also controls nozzle movement and the nozzle position also controls firing air, but only for one of the two firing stages. In the two-stage system the nozzle travels a certain distance, then begins to allow airflow through the bore. After traveling completely a secondary firing port opens to allow increased flow. This second stage is made possible by an integral flow control system which also has the added benefit of allowing the optimal nozzle speed in each direction. The forward speed of the nozzle can be restricted without limiting the rearward speed of the nozzle.

In addition to the flow control and 2-stage firing, F1 also uses a custom solenoid designed specifically for this application. This allows the solenoid to become an integral part of the system rather than just a switch to control airflow. The advantages include a more compact system and a more efficient system due to the reduced internal "Dead Volume".

Fusion Engine

If there are issues with the selector and semi/auto modes the first place to check is the FCU settings. Beginning in firmware 1.4 and later any fire mode may be assigned to any selector position. This allows the possibility of any combination of fire modes (including SAFE-SEMI-SEMI). Before checking anything else, make sure that the FCU is not set to SAFE-SEMI-SEMI.

If the FCU settings are correct than it is likely a physical problem where the selector switch is not being activated, or a damaged component is preventing the completion of a circuit.

When the selector switch (located on the switchboard) is actuated it completes a circuit to ground. The FCU reads this as a digital "0" and knows it is now in the S1 position. Selector position S0 is the "switch open" position.

If the selector switch is not being actuated, the circuit will not be completed. Verify that the selector plate actuates the switch as it moves. Depending on the gun model it may be necessary to use the original selector plate from the AEG gearbox.

If the selector switch is functioning properly then it is possible that a damaged wire is preventing the completion of the selector circuit. Visually inspect the wire harness for damaged or broken wires.

Unfortunately, no. The Mini FCU was designed to work with single-solenoid systems like JACK and F1.

Although it shares the same connectors and 5-position wire harness it is only able to control one solenoid. The "unused" solenoid wire has been repurposed as an additional input in order to allow the Mini FCU to work with 4-position selectors.


Most likely, yes. F1 was designed to fit virtually every AEG gearbox available, including those with offset nozzles. The only things to determine are the correct nozzle and switchboard.

For most applications a JACK/F1 switchboard is already available to drop directly into the gearbox. If no switchboard is currently being made for that model, plugboards are available for custom wiring.


JACK is a centerline AEG cylinder replacement. If the gearbox uses a standard piston and cylinder assembly and the nozzle is centered in the cylinder there is a good chance JACK will fit.

In order to install JACK into an AEG, the correct nozzle is required. PolarStar manufacturers a number of different JACK nozzle lengths to cover a wide range of guns. If the nozzle length you require is not already in production, custom nozzles can be made upon request.

In addition to the nozzle, JACK must interface with the selector and trigger of the host gearbox. This is accomplished using various switchboards which install into the gearbox shell.

For more information on the compatibility of specific models please see our Compatibility Guide in the support section.

FCU / Settings

A 7.4V LiPo battery is recommended for powering the FCU. Since the battery voltage is be regulated and reduced to 5V additional voltage is unnecessary.

9V Alkaline batteries should not be used as they do not provide sufficient current to power the solenoid.

All PolarStar FCUs may be set to a semi-only mode through the selector settings.

In instances where the replica must be permanently converted, semi-only firmware is available for each PolarStar FCU model (Standard, Mini and Bluetooth). This restricts all selector positions to a single shot per trigger pull and the ability to adjust it has been removed.

Control units may be ordered with this firmware pre-loaded. Users may send in their current FCU to be re-flashed.

To correctly set the dwell on either the F1 or JACK you would first set your dP to the maximum setting of 99 and then adjust your air pressure until you are shooting at the desired velocity with the BB weight you will be using. Now start reducing the dP by 5 at a time until you see the velocity decrease or become noticeably inconsistent. This is a sign that you are under voluming the barrel so that air flow is being shut off before the BB reaches the end of the barrel. Increase the dP by 1 at a time until the velocity and shot consistency returns to where it originally was and then set the dP 2 higher than that point.

The "iS" is the anti-stiction timer. Each number has a value of 10 seconds (i.e. 01 = 10sec, 02 = 20 sec, ect.). The timer will begin after each trigger input and once it ends it will add the value you have set in "iP" to your "dP" for the first shot.

Therefore if you have "iS03", "iP10" and "dP50", after the system has been idle for 30 seconds it will automatically increase your dP to 60 for the first shot and then lower it back to 50 for the following shots until the system has once again sat idle for 30 seconds.

Note that if you have nothing set for your iP (i.e. iP00) then it will not add an extra plus to the dP regardless of what you have iS set to. The iS is simply a timer.

Air System

We only recommend running our system on HPA or Nitrogen. Liquid propellants such as CO2 could potentially damage the system if used incorrectly so we do not recommend its use.

The SLP rigs require that you use an HPA tank that has a SLP (Super Low Pressure) regulator. All tanks have an integral regulator that takes the tank's raw pressure (e.g. 3,000psi.) and reduces it to the output pressure of the tank itself (i.e. the pressure that comes out of the tank and goes into the air rig). This pressure is then reduced further by the regulator on the air rig which the tank attaches to. The SLP tanks produces 300psi or less while "traditional" HPA tanks produce over 800psi. Therefore you can only use a SLP air rig with a SLP tank so as to not over-pressurize and break the air rig while an air rig like the Redline SFR can use either SLP or traditional HPA tanks.

There are two basic types of HPA tanks on the market. The 3,000psi tanks are typically made from aluminum and are the least expensive of the two. However, the higher pressure 4,500psi tanks are carbon fiber so they are lighter and will last for more shots per fill than a 3,000psi tank of the same size.

About Us

PolarStar Airsoft was formed in 2009 as a part of PolarStar Engineering & Machine with the goal of bringing our engineering experience and focus on quality to airsoft. Since then, PolarStar has made innovative airsoft products of the highest quality, designed and manufactured in the USA.

PolarStar products, including the patented Fusion Engine are designed by airsoft players, incorporating airsoft experience with the feedback of the commnity.

Latest News

PolarStar F1Posted 2016-05-13
HPA Speed TriggerPosted 2016-06-23


PolarStar Airsoft
5 Garfield Way
Newark, DE 19713
P: (302) 449-4866