How to Make an Airsoft gun Shoot Slower Permanently

Airsoft is really fun, especially when  all players are playing fairly. One of the unfair and dangerous things you can do on the airsoft field is when you do not stay within the fps limits of the particular field you’re playing in. I’ve just finished watching video where a cheater was using a gun that was way too hot and almost injured another player. Different fields have different fps limits and you might be wondering how to make your gun shoot slower? I had this question myself and I did a bit of research and he is what I found.

The most effective way of getting your airsoft gun to shoot slower is changing the spring in your airsoft gun to an M100 M90 spring. This will reduce the amount of energy coming out of your airsoft gun and this will reduce your fps and keep you within the legal limits. (jump to this method)

FPS Restrictions

Average CQB arenas will require that you have an FPS<300 when you are using full auto and <350 FPS when you using a gun that has semi-auto. In outdoor fields, the requirement is that you shoot no faster than 400FPS  for auto guns and no faster than 450 for semi auto guns.

Below is a representation of the average FPS restrictions in Airsoft Fields

FIeld TypeAutomatic Guns FPS RestrictionSemi Automatic FPS Restriction
CQB Field300 FPS350 FPS
Outdoor Field400 FPS450 FPS

Now this  restriction on fps is based on 0.20g BBs.

the most important thing to consider when thinking about fps limits is not necessarily the fps but the amount of energy that the gun is shooting at. This is referred to as Joules. The reason for this is heavier bb’s will shoot at a different fbs but we’ll have the same amount of jules and this is the thing that s of fields will be measuring for.

Over and above the restrictions within the field, shooting BBs with a high of a amount of energy, even if they are below the FPS, can injure an airsoft player. It’s therefore important to be careful about the amount of energy coming out of your gun to make sure that you do not injure a player in your field.

Why is FPS Important?

BBs moving at higher speeds than what is generally allowed is likely to cause injury to an airsoft player. Some of the worst injuries would happen in places like the neck where most people don’t normally have protection on. An airsoft bb can cause serious injury especially if it penetrates the skin in a delicate place.

While injury from an airsoft bb is unlikely if it is shoot at normal speeds it becomes a different story if the limits are breached. This is why it’s really important to add here to the fps limits.

Then there is the part where you would be called a cheater and hated in your airsoft field if your gun is shooting too hot.

When you would need to reduce how fast your airsoft gun shoots

You would normally need to reduce the shooting speed of your airsoft gun in the following cases.

  1. When the gun modification you just did increased your fbs past the acceptable limits. You may have upgraded something in your gun that increases its FPS and you may now need to lower rate to acceptable levels.
  2. When you’re playing cqb with a gun that was designed for outdoor play. Cqb usually requires that your gun shoots at lower FPS. This is because the engagement is usually in close quarters than field play. This means that bb’s shots from the same gun will hurt way more and could cause more injury in cqb than when shot out in the field.
  3. If the gun you purchased has a higher fps than what is allowed on your field. Some guns shoot at high fps is right off the box. You may need to do some modifications in order to reduce they’re shooting speed to acceptable levels.

How to reduce the FPS on your airsoft gun

Below are the different methods of reducing the fps on your Airsoft Gun.

Replace the spring with a M100 or M90 spring  (Most Recommended)

The way this works is by dismantling your airsoft gun gearbox and replacing the spring that is currently there with a weaker spring that will deliver less energy when it is fired. the gearbox to your airsoft gun is a sensitive part and I would advise that you do not touch it unless you know what you are doing. It is easy to mess up the gear configurations within your gun and this may make your gun to start breaking gears and jamming up.

I would advise that you look for an airsoft tech that can be able to effectively dismantle and reassemble your gun to do this for you. As they do that replacement, you may probably want them to also shim your airsoft gun. Shimming is the signs of improving the efficiency of the gears in your airsoft gearbox to make more tightly fit but far apart enough not to generate unnecessary friction between the gears.

The M100 or M90 spring is going to help reduce your fps since it has had lower tensile strength than regular springs. Be sure to confirm of your gun will work with this spring before buying it.

The difference between the M100 and the M90 is the strength of the spring. The M100 shoots hotter than the M90 and you would choose one or the other depending on the amount of reduction to FPS you are looking for.

Cut your gun’s spring to reduce the fps (Not the best way to go)

Other than buying an m100 or m90 spring, the other option you have is to cut your spring in order to reduce its strength. The problem with this approach is that you are not guaranteed to reduce your fps to the desired level with this method. It may either reduces too much or not reduces enough and you are not guaranteed to get the results you would expect.

The way to do this is the same as the method above but this time you will not have to buy the spring.

I would not encourage you to go this direction since an average spring would cost roughly around $10 to $20.

Use heavier BB’s (Not Dependable)

shooting I have your bb will cause your fps to reduce since the force being produced will need to push a heavier bb which will cause its speed to be reduced.

In my research, i found that the force of the bb will still be the same but the speed will reduce. Since many fields measure Joules together with fbp, this method may not work for you seems so your fps will be lower, the amount of energy in your bb who remain the same.

In addition to this, most fields require you to use ammo provided by them while chronoing and you may be prevented from playing even when explain what you’re trying to achieve with heavier bb’s.

Break in your spring (May Not Work)

Another methods of reducing your fps is breaking in your spring by shooting several thousand rounds of bb’s. This method makes the assumption that your spring will reduce in strength due to wear and tear and therefore reduce your fps.

The problem I have with this approach is that you do not have guaranteed results of how many bb’s it would take to reduce your fps to the desired level.

I would probably try it if I am slightly past the limit but if you have a large difference between your fps and the field requirements, I would advise that you use the methods above.

How to replace the spring in your Airsoft Gun

If you would like to change the spring yourself, you will need to understand how the internals of your airsoft gun work to ensure that you know your way around your gun before ever starting to dismantle it.

A good way to go with me to view a video of your particular, being taken down for you to be able to understand all the parts and the mechanics of the internals of the your gearbox. here is an example video of an airsoft gearbox being taken down and a spring being replaced.

Some of the tools you will require are:

  1. Phillips Head Screwdriver
  2. Allen Key in the right size for the screws on your gun
  3. A flat head screwdriver

A word of caution on this:  Ensure that you actually know what you’re doing before you begin dismantling your airsoft gun. Understand how your gun works and make sure that you put all the small pieces in proper order to ensure that you do not miss anything during the reassembly.


Lowering your FPS to an acceptable level will help you protect the players out on the field and help avoid getting branded the “jerk” of the field and is definitely worth doing. Its also important to make sure that you stay safe and use the necessary safety precautions and  gear to ensure that you and your fellow players don’t get any injuries. I have written an extensive post on Airsoft Safety and its definitely worth checking out if you take safety with the seriousness it deserves. Here is the link.