Oct 06, 2025

SSX23 / MK23 / SSX303 Power Tuning Guide

SSX23 / MK23 has been designed to output 1J of power as quietly and efficiently as possible, but as time went on, people realised that this pistol is so silent and accurate that it can be built into a primary rifle. And with that, players have looked at ways to increase the power output to increase its effective range.

However, there’s a lot of confusion about how to tune the power on MK23 / SSX23 / SSX303 pistols. This guide breaks down every aspect and part that affects power output, explains how they interact, and explains how to get the power you want without wasted gas or a painful trigger pull.

What affects power output:

Ambient temperature - can’t affect but needs to be taken into account
Inner barrel length & diameter - directly affects power output
Hammer spring - the main internal spring that affects what strength of gas / PSI that can be used
Gas strength / PSI (including HPA adapters) - directly affects power output, but has caveats
Nozzle restrictors - only reduce power, useful for lowering FPS without changing anything else

1. Ambient Temperature

Ambient temperature on the game day is the one aspect that’s out of our control, but it can dramatically affect power output and efficiency of the pistol. There are different strength gases available for airsoft use, but the pressure will be dramatically different depending on the temperature; therefore, it’s important to use an appropriate gas for the temperature.

How it affects power output:

Warm weather will increase the gas pressure, while cold temperatures will drastically reduce the gas pressure
Too high pressure and the pistol will struggle to open the gas valve, and power output will actually drop (unless you upgrade to a stronger hammer spring)
Too low pressure and the pistol will struggle to shoot at all, and the magazine will not hold enough gas to make it through even 30 BBs.

How to work around it:

Use the appropriate gas for the temperature you’re planning to play in. These are recommendations for stock SSX23 / MK23 to achieve around 1J power output:

<0°C → pistol will not work
0°C to 5°C → Black Gas (super high pressure)
6°C to 10°C → Red Gas (high pressure)
11°C to 20°C → Green Gas (standard)
>20°C → Blue Gas (low pressure)

Using an HPA (high-pressure air) setup will allow you to use your pistol in any temperature because ambient temperature does not affect the pressure of air - this is also the only way to use the pistol below 0°C reliably.

TL;DR: For gas, use appropriate strength for the temperature (lower power gas in hot weather, stronger gas in cold). Use HPA to achieve reliable performance at any temperature.

2. Inner Barrel Length and Diameter

As with any airsoft replica, the inner barrel plays a significant role in the SSX23 / MK23 power output. A longer inner barrel can boost your power output, but only up to a certain point.

Based on our own and community testing, it’s been determined that the longest inner barrel that makes sense for this platform is around 300mm in length. Any longer and there is not sufficient volume of gas/air to push the BB through the barrel, and the lack of volume will start decelerating the BB.

Inner diameter (ID) of the barrel will also play a role, but it won’t be as noticeable since most pistols like SSX23 already come with a 6.02mm inner barrel, which is as efficient as it gets. That said, if you are picking out a new barrel for your SSX23 / MK23, know that picking a larger ID barrel, like 6.05mm or more, will likely reduce your power output.

How it affects power output:

A longer inner barrel will increase power output (but only up to around 300mm in length)
Tighter inner diameter barrels, like 6.01-6.03mm, will have better efficiency (slightly higher power output)
Widebore barrels like 6.05mm and higher will see a slight but noticeable drop in power output

How to use it to adjust power:

SSX23 comes pre-modified to accept longer barrels - if you have 150mm barrel, adding length is the easiest way to increase power
Most other MK23 versions (ASG/STTi/TM) need outer barrel modification (drilling) to fit longer barrels
Increasing the length from 150mm to 300mm will see a ~50% increase in power output
The MK23 / SSX23 platform uses VSR10-style inner barrels, of which there is a wide range of options to choose from
Requires a longer suppressor or outer barrel extension, or you will be making your replica louder

TL;DR: Use a longer inner barrel to increase power, but only up to 300mm in length. SSX23 will take longer inner barrels out of the box, while other MK23 variants will require modifications.

3. Hammer Spring

The hammer spring is the most crucial component in the SSX23 / MK23 trigger mechanism, and it’s also the least known about. Since the pistol is a non-blowback replica, the trigger is directly linked to the hammer and the hammer spring. This means that the hammer spring is the one component that controls:

How strong will the hammer hit the magazine output valve
How strong the trigger pull will be (there is no blowback to cock the hammer)

By default, the pistol was designed to be used at around 20°C with regular green gas to achieve 1J power output. But if you have ever tried using a stronger gas like red gas in a pistol, you will know that the power output actually drops!

This is because the backpressure on the output valve is higher than what the hammer spring can overcome. So to overcome this increased pressure, your pistol needs a stronger hammer spring. Thankfully, there are two ways to get your hands on a stronger hammer spring these days:

Getting the Stronger Hammer Spring Set by TRIDOS.DESIGN (set of 3)
Getting Novritsch SSX303 Trigger Box (which comes with a pre-installed 200% spring)

That said, stronger doesn’t mean better - installing a stronger hammer spring will also make your trigger pull proportionally stronger and decrease efficiency if using lower pressure gas / PSI than what the spring was designed for.

You need to find the perfect balance between hammer spring strength and gas pressure / PSI. And the only way to do this is by experimenting and seeing what works best for your pistol and your desired power output.

How it affects power output:

The hammer spring controls how forcefully the valve opens, but it also affects the trigger pull
A stronger hammer spring allows for stronger gas to be used, but needs to be in balance with pressure to be efficient
Using a too-strong hammer spring will dramatically reduce gas efficiency and make the trigger pull unnecessarily hard
Using a too weak hammer spring with stronger gas will fail to open the valve properly and reduce power output instead of increasing it

How to use it to adjust power:

There is no simple answer to which spring will be the best for you
Get the 3 different strength springs and test which one strikes the best balance for your setup
Pick one of the springs and do test shooting with different strength gases / PSI:

Install 125% to start off if you are sticking to green gas and want to increase power slightly
Install 150% to start off if you are building a carbine kit and want to dramatically increase power
Then, change to a different spring depending on whether you want to achieve a higher or lower power output

You want to find the perfect balance where the spring is just strong enough to open the valve consistently, just like the stock spring is balanced for green gas to output 1J

TL;DR: Hammer spring allows use of stronger gas or HPA, but needs to be matched to pressure to be efficient. The 3-spring set gives you the best flexibility to tune your replica.

However, stronger springs increase trigger pull and make follow-up shots harder. Too strong a spring can waste gas by over-opening the valve. Use the lightest spring that achieves your target power.

4. Gas Strength or HPA

Gas strength might seem the easiest way to adjust power, but it’s not that simple in reality - it needs to be picked according to ambient temperature, and your hammer spring needs to be matched accordingly.

As we already explained, gas will be drastically affected by ambient temperature, which is a common pitfall of any gas-based airsoft replica. The moment the temperature drops below 0°C, any gas replica becomes almost useless.

Most commonly, CO2 magazines are offered as a solution for gas blowback pistols to be used in cold weather, but due to the design of the pistol, no such magazines exist for the MK23 / SSX23. For a few years, Novritsch claimed to be developing one, but it never came to life, and that project got shelved.

Thankfully, there is HPA (high-pressure air) as an alternative way to power your replica to ensure consistent power output in any weather. There are two main ways you can HPA your SSX23 / MK23:

Replace valves on your existing magazines with HPA connectors, but will require the HPA line to be disconnected every time you reload a magazine
Use an HPA adapter that uses either MP5 or Shotgun shells as the actual BB magazines without requiring the HPA line to be disconnected

HPA might seem like a cumbersome and more expensive solution, but nothing is more frustrating than arriving in a field and your gun not performing well or failing to work at all. If you are using your SSX23 / MK23 often or even as a primary, and want it to be reliable no matter what, it will be a worthwhile investment.

The HPA regulator also allows you to tune the pressure extremely precisely compared to gas pressure, which will always be fluctuating depending on ambient temperature, and is available in only a couple of different PSI strengths.

How it affects power output:

Gas will always be affected by ambient temperature and can only be used above 0°C
HPA is not affected by ambient temperature and allows for more gradual PSI tuning
Correctly matched pressure (gas or HPA) to the hammer spring will increase power output

How to use it to adjust power:

Use stronger gas / higher PSI with a stronger hammer spring to increase power
Use a weaker gas / lower PSI with a weaker hammer spring to reduce power (without losing efficiency)
Consider switching to HPA to have perfect control over PSI in any temperature
Gas is still the only untethered way to use SSX23 / MK23, but it can only be used in warm weather

TL;DR: Match gas strength / PSI to hammer spring strength. Use a stronger gas only to compensate for the cold unless your hammer spring is upgraded. HPA is the only way to avoid issues with ambient temperature on this pistol.

5. SSX Nozzle Set (Restrictors)

Novritsch sells a product called the SSX Nozzle Set as an accessory for their SSX303, which is used to adjust power. However, it’s a common misconception that these can also be used to increase power - that is NOT true!

This nozzle set was introduced as an easy way to reduce power on SSX303 by offering nozzles with different-sized flow restrictors pre-installed. It restricts the amount of gas that is released on each shot and therefore reduces power output without needing the user to mess around with hammer springs or other aspects of the replica. SSX23 / MK23 already comes with an unrestricted nozzle.

The problem with using a restricted nozzle to reduce your power output is that your trigger pull weight will stay the same - it’s a hack to reduce the power, but it keeps all the drawbacks of using a too-strong hammer spring.

We do not recommend using these, ever. Unless you really need to quickly reduce power output on a game day temporarily, or don’t have the tools or space to change the hammer spring.

How it affects power output:

Nozzle kits use restrictors to REDUCE power output
Hacky way to reduce power output while keeping all the drawbacks from a stronger hammer spring

How to use it to adjust power:

Nozzle sets cannot be used to increase power, only to reduce power output
The number on the nozzle refers to the hole of the restrictor
SSX303 can be lowered to achieve the following power outputs by using the following nozzles:

0.8-1 Joule – 2.3 mm insert (labeled)
1.3-1.7 Joule – 2.7 mm insert (labeled)
1.7-2.5 Joules – unrestricted

Only use the nozzle set as a last resort to reduce power on a game day temporarily

TL;DR: Nozzle Set only reduces power output - only use for temporary power reduction. Trigger pull will remain heavy. Use a hammer spring to properly reduce power output - that way, you also get the benefits of an easier trigger pull and improved gas efficiency

Tuning Recommendations

Goal - Raise the power a little bit on your MK23

Drill the outer barrel and upgrade the inner barrel from 133mm to 150mm
Change to 125% hammer spring
Consider using a stronger gas.

Goal - Max power output for Carbine Kit build

Upgrade the inner barrel to ~300mm
Install 175% hammer spring
Use Black Gas / get HPA to increase PSI

Goal - Reduce power on the SSX303 / Carbine Kit build

Downgrade hammer spring (SSX303 comes with 200% spring)
Use a weaker gas / get an HPA to lower PSI
Use nozzle restrictors as a last resort

Goal - Play in any weather

Get an HPA setup

HPA adapter (Shotgun shells 30rd / MP5 mags 60-110rd)
Matching magazines
Line
Air tank
Regulator

Get a set of stronger hammer springs for fine-tuning power output

Key Takeaways:

Hammer spring is the key factor — it defines what gas/PSI you can use
Inner barrel length up to 300 mm gives easy, reliable power increases
Gas/HPA only improves power when matched to hammer spring strength
Nozzles only reduce power; they never increase it!
Temperature heavily affects gas; HPA avoids this issue
Always balance your setup

too weak spring → valve won’t open
too strong spring → heavy trigger + wasted gas

Conclusion

In the end, power tuning the SSX23 / MK23 / SSX303 is all about balance — matching hammer spring strength, gas pressure, and barrel setup to work together. By understanding how each component affects performance, you can fine-tune your replica for any role, weather, or field requirement. Take the time to experiment, and you’ll unlock the platform’s full potential without sacrificing efficiency or reliability.