Paintball Gun Leaking CO2: Why It Happens & Easy Fixes

Paintball continues to be a popular and competitive shooting sport where the goal is to shoot your opponents with gelatin-filled capsules to eliminate them from the game. These gel capsules burst upon impact in a variety of colors, making it clear that the person has been shot. Paintball guns operate based on pressurized gas or air, depending on the type of gun you use.

CO2 in a gaseous form creates pressure to allow for the high-speed firing of a paintball gun. Gas may leak because of a broken gas insert seal, or the air source adapter (ASA) is not screwed correctly. You can fix this by making sure the O-ring is intact, the ASA post is in place, and the parts are well-lubricated.

CO2-powered paintball guns are the original paintball technology to create enough pressure to fire a paintball up to 300 feet-per-second. This high speed is the result of liquid CO2 being converted into pressurized gas to attack your opponents at rapid speeds. With the proper care and maintenance of your gun, you can quickly identify leaks and fix them for continued use.

If your gun is leaking CO2, there is a good chance you will need to replace the O-Ring. In fact, damaged or worn-out O-ring is the most common cause for leaking CO2 gas in a paintball gun. Luckily that is very easy to fix and it will only cost you a few dollars. Here is a great collection of paintball O-Rings on Amazon:

Understanding Paintball Guns and Issues in Leaking

Paintball guns (also known as paintball markers) employ technology powered by highly pressurized air to fire paintball capsules at high speeds. The original paintball guns used CO2 to pressurize them and are still commonly used today. Understanding this technology makes it easier to identify and fix leaks, which are one of the most common paintball gun issues.

CO2 Technology and Preferences in Paintball Guns

Paintball guns come in two varieties: CO2-powered or air compressed. CO2 guns rely on a pressurized gas to shoot the balls at high speeds. With the proper fit and seal of a tank, CO2-powered guns can last for hours of gameplay. They are able to shoot over 1,000 paintballs for a 20 oz. tank (the most common sized tank used in a gun).

CO2 technology relies on the conversion from CO2 liquid to CO2 gas. When liquid CO2 expands into a gas, it cools in temperature. The cooling process actually slows the rate at which the CO2 can expand, which will decrease the pressure. If you fire your gun more rapidly, the colder it will get, and the shots will be less consistent. This is particularly challenging in the winter.

The type of paintball gun you buy will require one form of a pressure system or the other (some guns allow for both systems). Even the paintball venue may only allow for one type of system to be used for consistency among players. Mechanical paintball guns rely on either CO2 or compressed air. Electric paintball guns are not compatible with CO2 tanks.

While more and more guns are using air compressors, CO2 tanks are inexpensive and fairly easy to find. They have a much lower initial cost compared to guns that rely on air compressors. You can also refill these tanks at a variety of stores, including hardware and welding shops if you are not near a paintball store. Sporting goods stores will also sell CO2 tanks or refill them for you.

Why Does CO2 Leak In A Paintball Gun?

Leaking is a fairly common problem experienced by users with CO2-powered paintball guns. With many pieces and accessories in a paintball gun, there are many crevices and areas that could be lacking the proper seal. This problem can typically be fixed with simple adjustments and replacements, which should be tried first before taking more drastic measures.

O-Ring Condition

Damaged O-Rings are the main causes of CO2 leakage.

O-rings are found throughout paintball guns as a seal to prevent air from leaking out of the gun. They allow the air to build-up to the pressure needed to fire the gel capsule from the gun. There is an O-ring where the tank of CO2 attaches to the gun. This ring needs to be attached properly and intact for air and CO2 not to leak out of the paintball gun.

This ring is attached to the nozzle of the CO2 tank and is crucial to the proper fit and seal between the tank and the weapon. One of the main causes of CO2 leakage is a problem with the O-ring.

There are multiple ways in which this ring can be damaged:

  • CO2 exposure: With increased exposure over time, CO2 can cause the O-ring to dry out and potentially crack. When this happens, the seal is compromised. Lack of durability within the O-ring will cause CO2 leakage.
  • Lack of cap: The O-ring can lose its function much more quickly when CO2 bottles are kept in a space where its nozzle can rub up against other items. Using a cap on your CO2 bottle will protect the O-ring and allow the seal to be tighter. This leads to longer playtime with less air leakage.
  • During play: Hitting the gun against something or dropping it can lead to damage of the O-ring and require replacement
  • Wrong air tanks: Make sure you are using the proper air tanks that are recommended for the specific gun you are using. The wrong air tank typically means it has too high of pressure and puts a great deal of stress on the O-ring and accessory pieces.

O-rings are located in multiple locations on a paintball gun. The two most common areas where you can experience leaks are on the front of the gun and down the barrel of the gun. The front of the gun is prone to leak if the O-ring is not functioning on the front volumizer (extra air chamber for higher firing rates and drop off). The barrel is related to the air source adapter.

Air Source Adapter (ASA) Fit

Air Source Adapter controls the flow of air.

The CO2 tank needs to fit snuggly into the gun to allow for proper transfer of gas and functional firing. The air source adapter (ASA) is a threaded port (entrance) for the CO2 tank to fit into your paintball gun. More traditional ASA’s allow you to screw in the tank, which can lead to damages when you want to replace or remove this tank.

Leaking can occur when the CO2 tank does not fit properly into the air source adapter. This can be caused by a faulty O-ring on the tank for any number of reasons mentioned in the previous section, or a more complicated issue with other accessory items. There is a pin in an ASA that pushes down on the tank valve to allow pressure into the paintball gun.

Lack of care in handling the gun and removal of the CO2 tank may lead to damages to this pin, threading within the ASA, and the O-ring. If replacements are made and the leaking does not stop, this suggests there is a problem with the cup seal. With extended use, the cup seal down the barrel, which also assists in sealing air, can cause leaking down the barrel of the gun.

Damages to the threading on either the ASA or O-ring will not allow for the two mechanisms to properly fit into one another. With increased force, these threads can be stripped, and increased friction can create pockets where CO2 can leak out. Always be mindful and careful when screwing in your tank to the ASA as these damages lead to leaking.

How to Fix A Leaking Paintball Gun

Now that we’ve walked through the issues that could be causing your paintball gun to leak, let’s get to fixing the problem. Not only does this section map out how to fix your gun’s current leaking problems, but it also offers insight and advice into preventing leaks in the future. Taking care of your gun with routine actions will eliminate leaking risks.


If you notice CO2 leaks on your paintball gun, the damage has most likely already occurred. We know the main causes associated with leaks now (O-rings, cup seals, and air source adapters) and these areas should be checked for wear and tear. You will most likely have to replace them to prevent future leaking issues.


The O-ring is one of the main culprits in CO2 leakage as we have discussed. Once the O-ring is clearly broken or damaged, it must be replaced. Having a couple of extra O-rings on hand is a good idea so you can quickly change it out once you see any damages. These are typically sold in a large pack with a variety of sizes and variations.

There are some considerations you should make when choosing O-ring replacements:

  • Size: You must make sure you are using the proper sized O-rings to match the size of your tank as well as the size of the ASA or the volumizer. Using the wrong size will inevitably prevent a proper seal from forming (which leads to leaks) or cause the O-ring to deteriorate quickly.
  • Thickness: The thickness of an O-ring is also related to fit. A thicker O-ring may be more effective in creating a seal if it can properly fit within the gun technology.
  • Durability: Beyond thickness and size, the strength of the O-ring’s material is also important. Many O-rings that are easily damaged are often too soft and may break or crack when trying to secure them into the gun.
  • Material: O-rings in paintball guns are usually made with buna or urethane. Buna is a rubber compound that is typically black. Urethane comes in a clear to white-yellow color. Guns will typically come with urethane rings as they are more durable and will usually last longer than buna. Both are suitable options for a paintball gun, but urethane can be more expensive.

To replace the O-ring, you can cut it or pull it from the tank using some form of sharp object. It is crucial that you are meticulous and careful in this process as the sharp object you use could scratch the metal on the tank (leading to more problems on your hands). You can then put the replacement O-ring on the tip of the tank nozzle or volumizer (depending on location).

When replacing the O-ring, make sure you are using ones that are recommended by the manufacturer of your paintball gun. This will ensure that they are the proper size and fit for the specific gun and tank you use. Using generic O-rings may lead to premature damage and waste gas.

How to replace the O-ring
Air Source Adapters (ASA)

There are multiple issues that can arise with an air source adapter and require replacement. Related to leaking, the threading of the port and the pin inside the adapter must be intact. If there are damages to either of these, the air source adapter must be replaced. More traditional air source adapters use a post that will press against the pin in the tank to release the gas.

Stripping of the air source adapter and damages to the post that allows for the release of gas will require replacement for efficient and proper use.

The best way to prevent future damages to an air source adapter is to switch to an On/Off ASA. Rather than relying on the pin to be secured snuggly into the tank, the On/Off mechanism will allow you to turn a valve that cuts off access to the gas. Then you can carefully remove the CO2 tank without any gas being released and limited wear being put on threading.

On/Off ASAs may also have a feature that allows the pressure to vent once it is turned off. This makes it easier to remove the tank from the gun. This is called a “bleed” or “purge” feature and may be worth the upgrade for convenience and maintenance of your gun moving forward.

How to replace ASA
Cup Seals

Many paintball gun users experience leakages that are not related to the O-ring or air source adapters. This problem may be more common in specific brands of a gun, but is a concern to be aware of in all mechanical guns that rely on CO2 gas. One of the primary reasons for cup seal replacement is the leaking of CO2 down the barrel of the gun.

They are fairly inexpensive to acquire and will save you lots of gas when replaced. You can replace a cup seal on a gun by following these steps:

  1. Remove screws from the bottom of the gun where the CO2 tank is inserted. This will help to remove the mechanism that allows gas to enter the barrel.
  2. Remove the screw underneath the barrel to completely remove the air regulator.
  3. Look into the barrel-side entrance into the gun to see the old cup seal. You can typically shake the paintball gun to loosen the cup seal, and it will pop out.
  4. Once the cup seal is removed, set the gun up vertically and drop the new cup seal into the chamber. You can wiggle and adjust the cup seal to have its screw enter the hole in the gun. It should fall in securely.
  5. Place the air regulator back over the cup seal and reattach the screws snuggly in both locations.

This is a simple and straightforward process that will fix 90% of leakage issues in the barrel of the gun. Your specific gun will give the specifications for the dimensions and type of cup seal to use. Your gun should also provide instructions on how to replace the cup seal that may be more specific to your style of the gun than the general directions mentioned above.

How to replace a cup seal

Maintenance and Prevention

Once you have replaced the mechanisms and parts that were causing the leaks, you should take some necessary steps to prevent leaks and maintain the usability of your gun. These will cut down on future costs and allow for less time working on your gun and more time shooting at your targets.

O-Rings Maintenance

O-rings will inevitably get worn out and need to be replaced with time. There are steps you can take to minimize premature replacement. Taking these actions will minimize long-term costs and allow your paintball gun to last longer. Faulty O-rings are a major cause of leakage and end up wasting CO2 if they are not properly fitted.

To keep your O-rings working properly:

  • Use urethane O-rings: While Buna is another successful alternative, urethane is longer lasting and a more durable option. You will not have to replace the rings as frequently if you spend a little bit more money and opt for the premier material.
  • Oil your O-rings: While you shouldn’t overdo it, oil your O-rings located on the front and rear bolts before game play. O-rings get damaged because they dry out and crack. Keeping them oiled will maintain their durability and slight pliability. This should be oil that is specifically used for paintball guns as random oils can damage the O-rings. Too much oil will build up, causing delays. Your manual should specify the type of oil used.

O-ring maintenance and replacement should always be in your mind when taking care of your paintball gun. You should routinely look at the O-rings for any cuts and tears that could be letting air leak or compromise a tight seal. Replace the O-rings immediately when you see these damages to prevent leaks the next time you play.

Air Source Adapters Maintenance

Keeping your air source adapter in good condition is important to ensure that the gas from the CO2 tank can be successfully transferred into the barrel of the gun. The main way to do this is to make sure that you carefully insert the tank with a proper O-ring to prevent any stripping of the threading.

If you do notice that CO2 is leaking down the barrel of the gun and aren’t convinced that the cup seal needs to be replaced, you can try putting a little oil in the air source adapter. This may help to allow for an easier fit between the ASA and the tank, and it is only a temporary fix that will probably not prevent leaks from happening in the future.

On/Off ASAs are easier to maintain as the technology allows for easier removal of the air tank. This will prevent stripping and damages to both the threading and post in the ASA as well as the O-ring and pin inside the tank that allows for air to be released.

Removing A Paintball Tank From The Gun

Most of the issues related to leaking CO2 occur as a result of a paintball gun tank being removed from the gun. You should remove the tank after every use, making the exposure to damage greater with improper use.

To remove a tank from a gun, you should:

  1. Make sure all paintballs are removed from the gun as well as the breach (the area where the individual paintball loads into and sits before firing).
  2. Put the barrel cover on and point the barrel away from yourself and others for safety.
  3. Carefully untwist the tank, making sure you are doing this slowly and not putting pressure on one side or the other to prevent scratching and stripping of metal. This should be done while holding down the trigger to dry fire quickly. You fire this to release all the air that is still pressurized inside of the gun.
  4. Once all the air has been removed from the tank, you can fully remove the tank from the gun.
  5. Put the cap on the CO2 tank to prevent damage to the nozzle of the tank. Make sure you store your tank in a cool area and not expose it to heat as the gas expands.

As mentioned, this process should be completed after every use of your gun. Keeping the tank on the gun will keep a consistent build-up of pressure which can be hard on the gun and the tank. The pressure can create a leak, which is what we are trying to fix in the first place!

If you have an On/Off ASA with the bleed or purge feature, you can simply turn off the tank and remove it. This advanced technology is much easier on your equipment and prevents damage associated with constant tank removal.

How to safely remove a paintball tank from the gun

Checking For A Paintball Gun Leak

Sometimes you may not know that CO2 is leaking from your paintball gun because it is releasing at a slow and faint rate. Periodically checking for leaks will make sure your gun is operating properly and you are not losing gas unnecessarily.

There are two main ways to check for leaks:

  1. Listen for escaping air: In a quiet environment, you should be able to identify where escaping air is coming from. There should be a hissing sound or what it would sound like if air was being let out of a pumped ball or another pressurized air environment.
  2. Bubble test: You can also put a little bit of soapy water on areas that could possibly leak. If bubbles start to appear around the area, then this suggests a leak. Larger bubbles mean larger leaks.

You should definitely run your gun through these tests after an accident or mishandling of your gun. These are the times when your gun would be most susceptible to leaks. Checking for leaks before it is obvious that they are happening is a good strategy in gun maintenance and care.

Keeping Your Paintball Gun Free From Leaks

We’ve discussed that paintball gun leaks are often caused by faulty O-rings, broken cup seals, and air source adapter (ASA) damages. You can easily replace all of these when they deteriorate or become damaged, stopping both leaks and the wasting of CO2 gas. Replacement is the most effective fix for CO2 leaks in paintball guns.

There are measures you should take to prevent the need for these replacements in the first place. Proper paintball gun care and maintenance will prevent damages to these pieces. Making sure you keep the O-rings well lubricated, carefully removing the tank from the air source adapter, and removing the tank after every use are necessary for proper functioning.

Beyond this, there are a couple of key things to remember when taking care of your paintball gun:

  • After removing the CO2 tank from the gun, keep it in a cool space away from heat or sun.
  • Put the cap back on the CO2 tank to avoid damage to the threading on the cap.
  • Clean the paintball gun from paint debris, oil, and dirt. This will keep the gun from developing build-up, especially in areas that require tightening and sealing. You can do this with just a wet towel and then dry.
  • You should oil the O-rings and bolts after every use to prevent rust.

Participating in paintball is a fun and competitive activity to play with your friends. You want to make sure that your equipment can fire the most efficiently, and this means no leaks! Keeping these precautions and fixes in mind will allow you to keep your gun in top condition and enjoy even more time spent at the field instead of on the sidelines!