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How to choose the right Systema gearbox for you?
An example of a 1J High Speed gearbox for the TM M16A1 and VN. (GB16R-1J-0)
An M120 Torque Up gearbox for the TM M16A1 and VN. (GB16R-12-0)
A front-wired version of the M120 Torque Up gearbox. Fits the Tokyo Marui XM177 and CAR-15. (GB16F-12-X)
1J High Speed gearbox for the Tokyo Marui XM177 and CAR-15 (GB16F-1J-X)
An A2/SR-16 version of the 1J High Speed gearbox. Notice the rear-wired configuration, and cuts in the rear of the gearbox. (GB16V25R-1J-0)
This gearbox is for Tokyo Marui M16A1/VN models only. Features an M150 spring and a FET switch in line with the wiring. (GB16RD-15-0)
An M150 gearbox for the MP5 series. Notice the ported Bore-Up cylinder. The FET switch requires a solid stock or battery bag. (GBMP-15-X)
Turbo version of the MP5 gearbox. Achieves the highest speeds and includes a Turbo motor as well! (CMB-T-MP)
M170 Magnum gearbox for the G3 series, excl. PSG-1. Includes a FET switch and a full cylinder for full length barrels. (CMB-M-G3)
This M170 Magnum gearbox suits a rear-wired SR-16 and other M4 series. Cylinder ported for a 363 mm inner barrel. Also includes a FET switch. (CMB-M-SR)
A rear-wired Turbo gearbox for the SR-16 or M4A1 with a rear battery configuration. (CMB-T-SR)


The easiest way to upgrade your AEG is not to open up the gearbox in the first place, but to replace it with a completely tuned model with the best parts already installed. This route also has the benefit of being able to reverse easily, and you will have a stock gearbox handy for a retrofit, in case you need an even lower velocity for CQB. But how do you choose which one is the right for you in terms of output energy, and what else should you consider when choosing a ready-made gearbox?

General principles

No matter what series your AEG is and regardless of the desired power level, the barrel length and cylinder type should be matched for optimum performance. That is why, for example, the MC-51 and other G3s have their specific gearboxes. If you are planning to extend the inner barrel of your MC-51, then you should choose a gearbox made for the G3. Then again if you're chopping a full length G3 down to a carbine, an MC-51 gearbox is the better choice. Remember that the cylinder tube can be changed easily to suit your needs, if you have an unconventional barrel length in mind!

There are gearboxes with various power levels, but the first thing is to choose a geabox that fits your AEG in the first place. The various models that use Version 2 gearboxes have different nozzles and selector plates, and other things to mind is the wiring (front/rear) and whether or not you need the rectangular opening in the rear of the gearbox.

MP5 and G3 series

The MP5 series are possibly the easiest models when it comes to choosing the gearbox: Excluding the MP5K and PDW, they all use the same gearbox configuration. Whether the stock is solid or telescopic, the gearbox is always wired to the rear, and uses an extension cord that leads to the front or rear of the AEG. It runs in the receiver instead of inside the gearbox, so thorough disassembly or soldering is not required to change the configuration. All MP5 series have the same barrel length, and even if you use a 300 mm inner barrel in your SD (as opposed to the standard 229 mm), the same cylinder is still suitable.

The G3 series bear a resemblance to the MP5 series, with the exception that there are short and long models, so you need to keep the barrel length in mind and look for the right cylinder for your gun. The G3 series are also simpler and faster to disassemble, so installation is especially easy with these!

M16 / M4 series

The M16 series can be divided very roughly in two: Old type and new type. The old ones are only made by Tokyo Marui, and the main differences to new models are the nozzle and gearbox holes. The new types starting from M16A2 introduced the ability to tilt the receivers open realistically after removing the takedown pin. This requires two rectangular holes to be cut to the sides of the gearbox to allow the upper receiver tabs to slip up.

Nozzle
All M16 type models and receivers from other manufacturers like G&P, CA, HurricanE and G&G have a new A2 type nozzle. For example the CA XM177 uses an M4 gearbox, even though there is an XM/CAR gearbox in the selection, and the M15A1 uses an A2 type gearbox, not an M16A1 one. These AEGs don't need the rectangular hole in the gearbox for takedown, so a switch of the nozzle allows you to adapt old A1/XM/CAR type gearboxes to be used.

Wiring
A second difference is made by the wiring: Models with a solid stock have the wiring led to the rear, telescopic stocks that can't hold a battery require the gearbox wiring to be changed to the front. Instead of running an extension cord from the rear of the gearbox to the front, these gearboxes are configured to have the wiring exit from the front, right above the trigger. Remember that with a high power upgrade, a small battery inside the handguard is insufficient to cycle the mechanism properly.
The more powerful (M150 and up) gearboxes have a FET unit in line with the battery leads, so it is not suitable for a front-battery installation. A FET acts as an electronic relay, and eliminates arcing of the trigger contacts as well as reduces recistance in the power leads.

 

1 J High Speed

Output energy: 1 Joules (328 fps / 100 m/s with 0.2 gram BBs)

Many CQB arenas have strict velocity limits, which is understandable and mandatory for increased safety. The tempo of the game is high speed, and that is how your gun should shoot as well: Not that hard, but lots of BBs per second. 1 Joule high speed upgrades are the most popular choice in Japan, where the output energy is strictly regulated to 0.98 Joules. It is not uncommon to see AEGs shoot over 20 and up to 40 BBs per second!

The intake and exhaust parts of these gearboxes are optimized for high speed shooting at 1 Joules, varying slightly depending on the exact barrel length. 1J gearboxes are especially suitable for SMGs like the MP5, or similar sized assault rifles like the M16-derivant M733, and MC-51 from the G3 series.

We recommend 8.4 volt or 9.6 volt batteries with the 1 J gearboxes for optimum performance. A higher voltage could potentially turn the gears fast enough to catch the piston on its way forward, especially if combined with a Turbo motor!

Turbo

A close relative to the 1J High Speed gearboxes is the Turbo gearbox and motor set. They use an M100 spring instead of the 1J spring, and a slightly undersized cylinder to increase piston speed while keeping the velocity at 300 fps with a 0.2 gram BB. This configuration allows to achieve the highest ROF of the Systema CMB series.

 

M120 Torque Up

Output energy: 1.49 Joules (400 fps / 120 m/s with 0.2 g BBs)

The standard general gaming velocity limit at most sites worldwide is 400 fps. This upgrade offers extra range that is useful in more open woodland areas, while staying quite safe: From a distance of 6 meters (20 feet), the energy of the BB has dropped to 1 joules.

The stiffness of an M120 spring is 100% on top of a standard Tokyo Marui spring, while the velocity is increased 50% over the original. The laws of physics state that when velocity is doubled, energy is quadrupled. From this point of view you realize easily how much more stress the mechanism and motor are handling, so the adjustment of gear ratio comes into question. This allows the gearbox to be cycled easily even with a small type battery, yet you have the option of compensating the ROF with a higher voltage battery.

We recommend to choose a 9.6 volt battery if the size is small, but with Large cells even 8.4 volts will suffice easily. Large batteries of 9.6 volts are the most popular option.

 

M150 Super Torque Up

Output energy: 2.25 Joules (492 fps / 150 m/s with 0.2 gram BBs)

The M150 is definitely in the major league of upgrades, at the narrow top of the performance pyramid. Yet a common sight in the hardcore fields of Asia and Hawaii, it is not seen as often in western countries due to strict velocity limits. More often than not, users of an AEG shooting this hard are required to use semi-automatic mode only, and sometimes to mechanically restrict full auto from being selected at all! Great care should be taken when using high powered upgrades like this, but in turn they offer fantastic performance and range.

The M150 gearboxes are equipped with Bore-Up cylinder parts. Contrary to popular belief, it is not about air volume to handle long barrels, but rather about the compression speed: As the area of the piston head is increased, it pushes more air for the same piston travel compared to a regular (N-B) cylinder set. This requires a strong spring to keep the piston speed stable, and will work optimally with barrel lengths of 350 mm and longer. Do note that the exhaust nozzle of the cylinder head is enlarged as well, so regular nozzles will not work.

According to our experience, an M150 upgrade built this well does actually cycle even with a 8.4 volt battery, but there is one important point you should not overlook: When the battery power depletes as the AEG is used, it will soon drop low enough that the current demand from the motor is increased over specifications. To keep unwanted loads off the electrical parts, it is advisable to use a higher voltage battery. It allows the motor to turn the mechanism with ease, and this way eliminates current spikes. We recommend 9.6 - 12 volt Large type batteries for these gearboxes.

 

M170 Magnum

Output energy: 2.88 Joules (557 fps / 170 m/s with 0.2 gram BBs)

If the M150 was already at the narrow top of state of the art upgrades, then the M170 is the sharpest spearhead around. What makes the Magnum gearbox especially interesting from the point of view of an experienced AEG-tuner, are the gears. Previously this kind of springs could only be driven with Infinite Torque Up gears, which provided the necessary torque to compress the spring, but also lowered the rate of fire a lot. With the introduction of the Magnum motor, it became possible to drive the M170 spring with Super Torque Up -gears. Combined with a 12 volt battery, this provides a rate of fire never seen before in an AEG of this power level!