How to Change Your Airsoft Gun’s FPS

airsoft gun being chronographed at the Forest City Surplus airsoft range in London Ontario Canada

How fast is your airsoft gun firing?

There are many situations where you may want to change the FPS of your airsoft gun. The most popular being so that your gun can be played on a specific field. Since we are in the London, Ontario, Canada area we will continue this guide on changing your FPS keeping in mind the FPS speeds allowed by nearby fields. We will use the Flagswipe Paintball outdoor field, War Pigs Indoor arena and Mach 1 indoor CQB field.

Increasing to the highest FPS with full auto still allowed

The outdoor field we will use as an example will be Flagswipe Paintball’s outdoor airsoft/paintball field. The max FPS they allow here for airsoft, while still being allowed to shoot full auto is 400 FPS. We will use a G&G CM16 Raider as the example weapon for this situation. This is my personal airsoft gun, and I have personally bought entirely new internals for this gun, except for the gearbox and the gears themselves. This gun started off around the 360 FPS range (give or take 5 FPS) which was a perfectly acceptable start point. We need to gain 35 to 40 FPS to max out. My preferred route would be to do a spring upgrade and to get new piston, and cylinder heads. This would be the easiest way to achieve the new speed, although there are some other methods we could use. This gun comes stock with an m120 spring, which we would upgrade to an m125 spring. This should gain us about 10-15 FPS. This spring is not so much stronger that you need to worry about your other internals wearing down much faster; they will be able to withstand the spring. Then we want to check our air seals. We can easily check this by putting our finger on the cylinder head escape hole then compressing the piston, and see how much air escapes. This gun was fairly good in this regard, however I noticed that there was some slight air loss, so I chose to go for new cylinder head and piston head. For the cylinder head I chose a full aluminum head with double o-ring seals. It is very important to make sure you purchase the correct head for your gearbox. This gun has a V2 gearbox, so we got the V2 cylinder head. Then I decided to get a double o-ring piston head by magic box for my piston. This piston head also has ball bearings to allow you to get you the best force possible. Once both of these were in the gun I noticed about another 15 FPS was gained. Proper air seals really help the efficiency of the gun, as well as give you more consistent FPS. The last very beneficial internal upgrade we should do is a proper shim job on your gears, and grease everything. When I did this I took my time to make sure there was absolutely no grinding on the gears, and then I greased my spring, gears and piston. This just ensures that everything will operate with very little resistance. It will also make your gun much quieter to shoot as you will now only hear the motor whine and the spring firing. I got about a 5-7 FPS improvement by doing this which will put us right around the 395-397 FPS range. This allows for a slight variation in FPS from shot to shot and puts us right at the max edge. If you did not receive an FPS close enough to 400 with the last step of shimming and greasing, then I would recommend getting a tighter bore barrel. Make sure that that barrel is the same length as the old one. I then replaced the stock 6.05 mm width barrel with a 6.03mm tight bore barrel. This width will still fire full auto without any problems and should result in a 5-10 FPS improvement.

Dropping your gun’s FPS to play indoor airsoft

This section is for the players who have bought a gun and it is firing over 380 FPS. Most places such as Mach 1 Airsoft have a FPS limit of 380. Some indoor fields have even less like War Pigs (now closed) had a limit of only 350 FPS. Save yourself some hassle and make sure you check your field’s regulations for indoor before you make a decision on what parts you need to buy. I would say that if this is the situation you’re in then you should really just change the spring on your gun. Since you will be putting in a softer spring there really is no need to change many of the other parts which as all designed to work together. If you have already upgraded your other parts this means that your gun will be running more efficient than guns with stock parts. It can be hard to know exactly how much softer a spring you need to go, however I have found as a general rule you can expect 10-13 FPS loss per 5 spring strength you lose. For example if you went from an m120 spring doing 395 FPS, and lowered the spring to an m110 your FPS would be in the range of 370-375 FPS after the swap. You rarely need to upgrade all your internals for the lowering of FPS, just remember it can be very important to do so if you are going in the direction of raising FPS.

Another note to make is that you can always buy a gun that has a low FPS for indoor play specifically. Many people have an outdoor rig since they play woods ball most of the time, but it never hurts to keep your skills up during the winter. You can do this even buy purchasing the clear plastic guns. Even though they do not look as nice as the black plastic guns they will more than suffice for low FPS indoor play during the winter. Also it never hurts to have a clear pistol as a secondary. Many of these meet the FPS regulations for indoor, and can be useful for really tight corners. Do not underestimate clear plastic weapons when it comes to indoor play!

Getting your gun into the sniper FPS range (400-450 FPS)

Before I get started about this sort of a build, please note that this is to turn AEG’s into a DMR style build. Every gun is different and you need to take time and research what parts are best for you. This is my experience and I have been extremely happy with the results. I started with a G&G CM16 Raider as my base model. As I have said before this gun is a solid platform to build on, and although I am basically changing out all the internals I still really enjoy the gun as an affordable solid body to begin with. This is the list of internal changes I made to the gun, the outer appearance can be whatever your personal appeal is, and remember to make it your own!

So many of the parts I listed before I still use in this setup on my CM16. This build does require many more part upgrades because of the new stress the gun is under. I decided to go with a tight bore barrel. I found just the barrel I was looking for at an affordable cost with the 6.01mm x 455mm long tight bore brass barrel by DYTAC. This was going to allow my shots to be as accurate as possible. As this was a sniper rifle the goal was to tighten the groups I was firing. This now runs into a Modify fully metal hop-up unit. Your hop-up can be a fragile piece because the pressure from the cylinder head goes straight to it. So I decided to remove the plastic one and put this in. It should be noted that I left G&G’s stock hop-up nub in this setup. I also added 2 o-rings on the barrel that sit where the barrel and the hop-up connect to help with air sealing. As I stated before I added a modified cylinder head with double o-rings. The cylinder head has full aluminum construction just to make sure it can handle the force. This connects to the cylinder which was swapped to a light weight aluminum one by Modify, it is the enhanced one that is not ported. I changed the piston this time around to a Mad Bull PX piston that has full metal teeth. This was because I did not want the plastic teeth of the old piston to wear out since it is engaging the piston under much more stress than previously. I still used the Magic Box double o-ring piston head with ball bearings which works really well. I added an m130 spring by SHS. It should be noted that you should be careful when putting this spring into the gun, I did have it fly out once. On the end of the spring I now have a modified bearing spring guide which was for a V6/V7 gearbox. I did have to make some adjustments by grinding down the edges so it would fit. To do this accurately I used the stock spring guide to determine the best lengths while I was on the grinding stone. I still re-shimmed the gear box and greased all the insides to make sure it would work properly and without wear for as long as possible. Make sure that you grease the teeth on your gears and on your piston, it makes the gun much quieter and smoother. To top this entire build off I swapped the motor in the pistol grip for a SHS Ultra High Torque motor, because I wanted to make sure that it would be able to effortlessly pull back the new heavier spring. This motor did need a spacer to help it make good contact with the gears, and after a few adjustments to the pressure it was working smooth, and making great contact. After all this was said and done I am reaching 450-455 FPS on this M4 build. It can accurately shoot up to 225 feet with the hop-up being the only adjustment needed.

Forest City Surplus has all your airsoft needs right here in London, ON. Whether you need ammunition, sights, attachments, or beginner to expert guns, Forest City Surplus has some of the best pricing around. Remember to keep checking in as we get new stock in regularly, and it is constantly changing. You just never know when the perfect airsoft accessory for you will land in our store.

2 Responses to How to Change Your Airsoft Gun’s FPS

  1. George Li says:

    I agree that changing the spring is often the biggest part to your airsoft rifle’s FPS.

  2. Jeff King says:

    Any advice on how to up FPS on a PT99…???

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