High Speed Guide Part 1

Component Selection

Building a reliable AEG with a high rate of fire can be challenging. Achieving a high rate of fire (ROF) is actually easy, the hard part is to make it last. We recommended you start by aiming for a relatively mild ROF, then work your way up as your experience grows.

In an AEG, the ROF is set by the battery and motor. Other factors affect it slightly, but the battery and motor are your route into high speed. The rest of your work is to improve the reliability of the gun, allowing you to actually use it for as long as possible. With a lot of careful tuning, you will be able to build a skirmishable AEG capable of fearsome ROF.

In a high ROF gun, everything is put under more stress. This gives you a much smaller margin for error when tuning, as any mistakes will lead to part failure much faster. Aside from extensive research, the best way to learn is to just try something out and see what happens. Breaking something then inspecting the damage will tell you a lot about the finer points of AEG tuning, so you should be prepared to destroy a few parts as you learn. Using a chrono will easily allow you to measure your gun's performance; it is an essential tool in airsoft tuning. The Xcortech X3200 is the best choice right now.

Airsoft tuning is about choosing high quality parts and installing them carefully. Even the highest quality parts can be ruined by poor tuning. There is simply no way to build a reliable, consistent airsoft gun without putting a lot of time and effort into tuning it carefully. Part 2 of this guide will focus on tuning techniques.

Bearing that in mind, component choices are also crucial. You can do a perfect installation, but if you have a poor quality part, it will break, especially in a high performance build. This article will focus on choosing parts, with in-depth tuning guides to follow.



Your base gun should be made to Tokyo Marui specification. This means that it follows the dimensions of TM’s original AEGs and uses a standard gearbox. It is crucial  to choose a gun which uses the standard TM spec because these are the only guns which are compatible with a good range of high quality aftermarket parts. Guns which use proprietary designs, such as the Systema PTW cannot be upgraded for high performance because of poor aftermarket options.

Some good choices of AEG at the expensive end are G&P, LCT, VFC and King Arms. At the cheap end are JG, CYMA, KS and DBoys. The biggest difference between manufacturers is external quality. No company makes an AEG with consistently high quality internals, although JG motors are some of the best torque motors in airsoft and are frequently used as aftermarket upgrades.

Any AEG you buy as an upgrade platform will need several new parts, so we recommend just buying the gun you like externally as long as it adheres to the TM standard. Classic Army, Ares and KWA guns should be avoided as they differ from the TM standard and cannot be upgraded without a huge amount of extra work. Systema PTW guns are also to be avoided for serious upgrade work because of their proprietary design.

As to the exact gun model, the P90 is probably the easiest gun to work on. The gearbox can be accessed by removing just 2 screws. The front of the gun, containing the barrel group is even easier to remove, so the P90 is by far the fastest gun to disassemble and reassemble - something you need to do a lot when tuning. It uses a Version 6 gearbox which is well supported by aftermarket parts. KS are a cheap Chinese manufacturer who make an easily upgradeable P90.

Any other Version 2 or Version 3 AEG is a good choice too.

Before buying parts, you should fully inspect the gearbox to find out which parts need replacing. Many airseal parts such as the piston head, cylinder, cylinder head, air nozzle and bucking provide good airseal already, or can be easily improved to provide good airseal. If your gun is outputting consistent power, then your airseal parts certainly won't need replacing.


ROF is determined by your battery and motor more than anything else. They should be the first things you upgrade when building for speed. No airsoft guns are supplied with a good LiPo, so you will certainly need to buy one. 7.4V (2 cell) is a good introduction to high speed and we recommend you start with that. But you will soon want to upgrade to 11.1V (3 cell).

Always buy LiPos from a reputable brand. Turnigy make excellent, affordable LiPos. Most LiPos made for airsoft are very poor quality, so in general you should buy from RC stores. Although some airsoft retailers are beginning to stock Turnigy and other high quality brands.

As a general rule, you should buy the biggest battery with the highest C rating you can fit in your gun/battery bag.

An article on LiPos is on the way, but in the meantime you can find out all about them on Google. 


The motor must have neodymium magnets. You can easily tell if your motor has neo magnets by removing the motor from the gun and turning the shaft by hand. If the motor is difficult to turn, then it contains neo magnets. Stronger magnets provide a more powerful magnetic field, and this makes the motor capable of providing higher torque. These days neo motors are so cheap and so powerful that there's really no excuse not to use them. Trying to make a high speed build without one is virtually pointless. They come in two main varieties, 'speed' and 'torque'. Torque motors are generally preferred for most builds currently. Being more efficient, they run cooler and give better trigger response.

SHS and other cheap Chinese manufacturers make very good neodymium motors which are very affordable. SHS motors sometimes have inadequate glue on the windings, allowing the wires to come loose under centrifugal force, destroying the motor. Lonex motors are probably the best in their price class.

Electric system:

With your new battery and motor you're now transferring a lot of energy, and you need the electrical system to cope. Electrical resistance must be reduced as much as possible. Installing a MOSFET switch is the best single upgrade you can do for your electrical system. It will improve efficiency by reducing resistance, and save your trigger contacts from burning or melting. (More information is available on our MOSFET product page). Models without active braking are recommended in high ROF builds. You can reduce overspin mechanically, negating the need for AB which can cause unnecessary motor heat and wear. Replacing the stock mini Tamiya connectors with low-resistance connectors such as Deans, XT60s, Traxxas or bullet connectors is a very good idea as it further reduces resistance. Replace the stock fuse with a self-resetting polyfuse. They are cheap and last forever. (see our fuse product page for more information) Make sure there are no cold solder joints in the electrical system, as these increase electrical resistance and over time develop into faults. See our soldering guide for more information. Your electrical system should now be capable of handling the high current your motor will draw.

We sell MOSFETs and fuses designed specifically for high performance AEGs.



No airsoft gun comes with highly durable gears, so for the best reliability you should replace them. However they can sometimes perform well, so we recommend using them until they fail. To reduce downtime, you should have a spare set ready.

Siegetek gears are the only ones we currently trust. If you can't afford them, just buy the cheapest ones you can find, since anything other than Siegetek is relatively unreliable (at the time of writing). Lower ratios give higher ROF. Spend at least a full day learning how to shim them perfectly. You are going to put them through some serious abuse and correct shimming is vital to ensure they last as long as possible.

The correct way to shim gears is to start by setting the bevel/pinion interaction to be as smooth as possible. Setting the pinion position is done via the motor height adjustment screw, and setting the bevel gear position is done via shims. This can be done visually if you drill or cut a viewing window in the gearbox shell. Once the pinion gear and bevel gear are meshing correctly, you can shim the spur gear and sector gear.

A more in-depth article on shimming is in the works, but for now you can Google ‘bevel shimming’ for more information.



Personally we prefer bushings as they're more durable and harder to ruin. Lonex, TerminusX, Modify and Prometheus/Laylax are the only manufacturers who make truly durable bushings which can withstand the extreme hardness of Siegetek gears. If your gun came with bushings, you should use them but inspect them regularly for wear. If your gun came with ball bearings, consider switching to bushings at least until you learn how to shim. Ball bearings have a significant risk of failure so there is much less room for error when using them. They are no longer recommended by Siegetek for use with their gears.

Lonex, Modify, Prometheus/LayLax and TerminusX make the best bushings in airsoft, and are the only ones we recommend.

All bushings/bearings should be firmly glued into the gearbox shell.


This is a part of the gearbox very likely to break in a high speed setup, unless tuned correctly. It is also crucial to choose a high quality piston to start with. Most AEGs come with pistons which are not well suited to high speed, although it is a good idea to use them while you learn. Breaking a piston and inspecting the damage will tell you a lot, so we recommend using the stock piston but having a backup (ideally several) ready to go.

SHS and Lonex make excellent pistons. We recommend the SHS 15 or 7 metal toothed models, and the Lonex 10 metal tooth. The tooth rack must be firmly glued in place before use.

All pistons must be lightened as much as possible, a process known as ‘swiss cheesing’, which involves drilling a series of holes or slots into the body to reduce weight while maintaining adequate strength. Lightening is important as it reduces the strain put on the components as the piston is picked up by the sector gear. Imagine kicking a bowling ball instead of a football. Good lightening is essential for a piston to be reliable, and this is one of the reasons that any piston with a metal body is a bad choice in any build, but particularly for high ROF.

The angle of engagement (AOE) must be corrected (see the Sorbothane extended description for an explanation of AOE). The second tooth and part of the third tooth of the piston must be removed as part of AOE correction.


Piston Head:

In order to reduce the piston weight, the piston head must also be as light as possible, so avoid metal one. Also any bearings should be removed from the it. Instead, you should use a spring guide with bearings. Many stock piston heads are perfectly good, although all piston heads should have vent holes.



The stock spring is often perfectly good, but it is a good idea to have a range of springs in your workshop so you can carefully tune the power level to suit your needs. Many companies make good springs, such as Guarder, SHS and Lonex.

Spring guide:

If your gun came with a ball bearing spring guide, leave it in. If not, you should upgrade it to a model with a ball bearing. This is to reduce or eliminate rotational stress in the spring caused by twisting.


Sorbothane cylinder head buffer:

Sorbothane is probably the most cost effective upgrade you can buy for your AEG. It is used to correct AOE which improves piston lifespan and to absorb shock which improves gearbox lifespan indefinitely. 70D hardness is the best mix of shape retention and shock absorption. No AEG comes with a sorbothane buffer, so you will definitely need to buy one.

We sell pre-made sorbothane pads, with an in-depth description on the product page.


Tuning a gun without a chrono leaves too many unknowns. You will find your work so much more rewarding by being able to quantify it. It is an essential tool in an airsoft workshop. The Xcortech X3200 is an excellent choice. It measures power and speed, and can be set to various BB weights. It is accurate and reliable, and has a 1/4" thead on the bottom so you can mount it on a camera tripod.

Once you have high quality parts, you can actually start tuning. Part 2 of this guide will focus on tuning techniques. In the meantime, you can research tuning techniques in the forums at, where there is a vast collection of information. Spend as much time reading as possible, and you will find your tuning experience much more rewarding and successful.