CO2 and High Pressure Air (HPA) - (a.k.a. Compressed Air, Nitrogen (N2) or Nitro)

By Jordan Ricks
5-20-05
www.specialopspaintball.com

For over 20 years, CO2 has served as an inexpensive and easily accessible propellant for paintball guns. Though cheap and convenient, CO2 tends to be less effective than compressed air, and much harder on your equipment. The frustration however, is that compressed air is not readily available, and for many paintball players, CO2 is the only option for powering their markers.

In its original state, CO2 is a liquid. To function properly, liquid CO2 needs enough space and heat to expand into a gas, so it is important to not ‘overfill’ a CO2 tank. (Overfilling a CO2 tank prevents the liquid CO2 from fully turning into a gas before it entering your gun, causing the marker to ‘freeze up’ temporarily.)

As the liquid CO2 is converted to gas to propel the paintball from your gun, the high pressure of the CO2 inside the tank expands to the lower pressure inside your marker, causing your gun’s velocity to fluctuate or ‘spike’ dramatically. (For example, one shot may chrono at 275 fps, the next at 290, and the next 262.) The different speed consequently affects the paintball’s trajectory and your accuracy.

The CO2 also expands inconsistently because the process of converting to a gas causes the temperature of your tank to drop, and as the tank gets colder, it produces less pressure.

Rapid shooting also poses problems with CO2. Sustained, rapid firing can cause the temperature of your barrel to drop by more than 30 degrees. If a barrel temperature drops from 85 degrees to 55 degrees, the velocity of your marker is affected, and may be reduced by up to 25 percent or more. If you chrono at the standard 280 fps, the resulting temperature drop of the barrel translates to a reduced velocity of 223 fps. Naturally, this would greatly affect your accuracy as well.

In addition to affecting your marker’s performance, CO2 can also be hard on your equipment. As you continue to squeeze that trigger and maintain a rapid firing rate, the colder your tank becomes, and the less pressure it produces. Eventually, your gun may start sucking in liquid CO2.

When liquid CO2 enters your gun, the sub-zero temperature can break O-rings and plastic power tubes and damage air seals and other internal mechanics of your gun. The liquid CO2 causes air seals and other internals to ‘freeze up’, rendering you helpless for several minutes until the mechanics thaw out, which usually means you'll end up waiting in the elimination zone. Liquid CO2 may also prevent the hammer from fully re-cocking, resulting in an instant conversion of your gun to ‘full auto’.

Rapidly firing with compressed air does not adversely affect the barrel temperature, resulting in more consistent velocity and accuracy.

Compressed air (high pressure air/Nitrogen) is much cleaner than CO2, which means it is not as harsh on the internals of your gun. Compressed air is not stored in liquid form and does not pose any temperature problems. The air systems typically use a regulator that is preset at 850psi, meaning that your gun will get a consistent 850psi. ‘Freezing up’ does not occur and performance is not affected under sustained rapid fire with the use of compressed air.

The Positives of CO2

If you are looking for reasons to avoid converting to compressed air, here are two good reasons to stick with CO2:

It’s harder to find places to get your compressed air tanks filled. The typical air compressors found at your corner gas station are designed to fill tires and low-pressure air tanks, and can seldom exceed a pressure over 350 pounds per square inch (psi). Most paintball guns need at least 800-850 psi to function. Expensive compressors, such as those found in scuba shops, are needed to fill compressed air tanks. Some paintball fields or large paintball stores have compressed air, but unfortunately, not many – yet.

A second advantage of CO2 is that tanks are much less expensive than compressed air systems.

Solutions for Common CO2 Problems

There are several accessories that you can purchase to minimize the occurrence of liquid CO2 ‘freezing up’ your marker, as well as hardware to stabilize the pressure as it enters your gun.

An anti-siphon valve is a tube that is placed inside a CO2 tank to prevent liquid CO2 from entering gun.

An expansion chamber, also commonly known as an ‘X chamber’ attaches to the CO2 tank and the paintball gun to prevent liquid from entering gun and stabilize the air pressure. The expansion chamber improves marker performance by reducing or eliminating freeze-ups and also helps to stabilize the air pressure. (The expansion chamber is a good mid-range solution, but does not provide a complete ‘air-pressure solution’ like a regulator. Costs generally run between $20 and $70.)

A regulator controls the gas pressure that is released from the tank to ensure that a more consistent air pressure is fed to the gun. Regulators are generally the most expensive solution and range in cost from $50 to $100.

High pressure air is expected to become more readily available to paintballers in the future; however, the price still may never be as low as CO2. But if you consider gun maintenance issues and the cost of hardware add-ons, high pressure air is still a bargain.

Pounds per square inch (psi) refers to the capacity of your tank. Naturally, the greater the capacity of your tank, the more shots you can deliver. A 3000 psi tank delivers roughly 10 shots per cubic inch (i.e. 80ci = 800 shots), while a 4500 psi tank delivers about 15 shots per inch (80ci = 1200 shots). However, these figures vary considerably, depending on your air configuration, type of marker and equipment used.