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Written by: Michael Jarantilla
Written on: December 7th, 2003
Tags: sports & recreation, mechanical engineering
Thumbnail by: Shadowjin/Wikimedia Commons
About the Author
In the fall of 2003, Michael Jarantilla was a junior at USC majoring in Electrical Engineering. He enjoys playing paintball on the weekends.
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Volume V Issue V > The Changing Face of Paintball
At its essence, paintball is about marking other players with gelatin capsules filled with colored dye shot from a gun powered by compressed gas. While the fundamentals of the game have not changed since its inception, the technologies behind many of its principles have advanced. Fuelling this change is the development of newer, more sophisticated paintball guns that have evolved from single-shot, hand-cocked pistols into fast-shooting, electrically-powered precision machines. As a result of the advancement in marker technology, the game has been transformed into a fast-paced, high adrenaline tournament sport.

Introduction

Shadowjin/Wikimedia Commons
Figure 1: A modern-day paintball player.
Your heart pounds against your chest, your veins pump adrenaline, and your finger twitches nervously on the hair trigger of your $1,000 electronic marker as you wait for the head referee to start the game. He finally begins the countdown, but before he even finishes speaking, you are sprinting towards your destination, a three-foot-high inflatable bunker, hoping that you are not hit by one of the hundreds of paint-filled capsules being launched by the other team's battery-powered markers. This is how a game of modern tournament-level paintball begins. It has changed dramatically from the slow-paced, stealthy survival game for military and outdoor enthusiasts into a fast-paced, high-adrenaline extreme sport played in balanced, standardized arenas where bushes and trees have been replaced with balloon bunkers, and stealth and cunning have been replaced by speed and reflexes.
Fueling this change is the development of newer, faster paintball guns, or markers. More than any other competitive team sport, paintball depends on developing technologies to keep the game as fast and exciting as possible. Consequently, markers have evolved from single-shot, hand-cocked pistols into fast-shooting, electrically-powered​ precision machines. As a result of the advancement in marker technology, the pace of the sport has increased greatly.

Fundamentals: Firing A Paintball

Whether the marker you are using is a 1980s-era stainless steel Sheridan pump or a 2003 WDP Dark Angel iR3 with composite polymer internals and a computer interface jack, your ultimate goal is to strike a target from a distance. Due to air resistance and gravity, a paintball accelerated to the maximum legal muzzle velocity limit of 300 fps (feet per second) has a maximum range of about 120 feet and an effective range (the range in which it has enough kinetic energy to break the paintball on a human body) of around 60 feet. To reach this speed and range without prematurely breaking the paintball, all modern markers utilize compressed gases as propellants.
According to the Ideal Gas Law, one of the basic laws of thermodynamics, a pressurized gas expands uniformly until its pressure is equal to that of the surrounding gases [1]. Paintball markers take advantage of this law by using a canister similar to the oxygen tanks used by scuba divers and firemen to store a high-pressure gas. The canister screws onto an adapter on the marker called the air source adapter, or ASA, which has a pin that opens the valve in the canister to regulate gas flow into the marker's main gas chamber. A sealable valve connects the gas chamber to the breech where the paintball is held. When the marker is not being fired the valve is sealed to prevent the gas in the chamber from escaping. When the trigger is pulled, the cupseal is pushed forward, briefly opening the valve to allow a short burst of compressed gas to expand through the valve and into the bolt (the mechanism that channels the compressed gas onto the paintball).
The sudden difference in pressure between the air in front of the paintball, which is at normal atmospheric pressure, and the gas behind the paintball, which is under high pressure (typically 200-800 psi), causes the high pressure gas to exert a force on the paintball, pushing it forward as the gas expands outward through the barrel.

Acceleration: Impulse and the Venturi

One of the main challenges of firing a paintball is using a force that is strong enough to accelerate the capsule to the necessary velocity yet gentle enough that it will not break before it exits the barrel. Again, the use of compressed gases helps solve this problem. Because gas expands uniformly, the force a pressurized gas exerts is distributed evenly over the contact area, thereby reducing the force applied directly on the paintball while maintaining the force necessary to accelerate the ball. The average force applied to the paintball is further reduced by the fact that the gas continues to accelerate the paintball as it is already moving down the barrel. Even though the pressure of the gas decreases exponentially as the paintball travels down the barrel, it is still at a pressure higher than atmospheric pressure, so it continues to accelerate down the length of the barrel. This extended force is known as impulse [2].
In addition to the gas laws of thermodynamics, another feature that helps alleviate the pressure on the paintball is the bolt. There are two main types of bolts: Venturi and Open-Faced. Venturi bolts are used in high-pressure (500 - 700 psi) markers and have a circular pattern of holes drilled into the face. This pattern of holes helps break up the air stream and allows the gas to expand more evenly and smoothly.
Open-Faced bolts, which have no holes, are preferred in low-pressure markers that operate between 100 and 300 psi. At these low pressures, the effects of air streams are significantly lower than in high pressure markers since low-pressure markers rely on gas volume rather than gas pressure to propel the paintball.
A contrast between high and low-pressure markers is that in high-pressure markers the pressurized gas acts on the paintball for only a short time before it is released, so the gas must have a high initial pressure to accelerate the paintball to 300 fps. In low-pressure markers, however, there is a lower average accelerating force, but since the acceleration takes place over a longer period of time, the final velocity is the same.

Velocity Consistency: Snow or Air?

To ensure an accurate shot, the velocity with which the paintball exits the barrel must be consistent so that it may be intuitively known by the shooter. Since paintballs are shot with arching trajectories to achieve greater range, a consistent shot-to-shot muzzle velocity ensures that a paintball will always have the same range and trajectory.
Muzzle velocity is largely governed by a marker's air supply. Carbon dioxide, the first power supply used for paintball markers, is still the standard for recreational players despite its many disadvantages. At extremely high pressures, carbon dioxide can only exist in a liquid form, but in order to be used by a paintball marker, it must first be a gas. Unfortunately, the pressure at which liquid carbon dioxide evaporates, called the vapor pressure, is determined by the temperature of its surroundings. For temperatures below 60 degrees Fahrenheit carbon dioxide's vapor pressure is only 300-500 psi.
When in liquid form, the carbon dioxide can be siphoned into the marker's internal pneumatics causing the o-ring seals to freeze, crack, and leak, effectively putting the marker out of commission until it can be repaired. Liquid carbon dioxide is known to be present in a marker when white vapors or flakes, called snow, spurt from the barrel. At high temperatures, liquid carbon dioxide can still enter the marker, but instead of being ejected as white flakes, it expands rapidly in the marker's main chamber. The sudden rise of pressure in the main chamber causes the velocity to suddenly spike, which means that not only could the velocity exceed the 300 fps limit, but also that it could cause an unpredictable trajectory or force the ball to break in the chamber, splattering paint down the barrel. This paint, if not cleaned, will cling to future paintballs being fired and cause them to curve dramatically.
Recently, compressed air has begun to replace carbon dioxide as a recreational power supply and in tournaments has replaced it all together. This is mainly because compressed air is not as volatile, or temperature-dependen​t, as carbon dioxide [3]. Unlike carbon dioxide, compressed air does not need to transition between physical states to be used as a propellant. Instead, it only needs to expand, and as air expands uniformly, pressure is kept more constant. While velocity deviations of as much as 20 fps have been recorded with carbon dioxide, velocity deviations using compressed air rarely exceed 10 fps [4]. The installation of an inline regulator, which is already standard in more expensive markers, reduces the variation even further by monitoring and stabilizing the pressure inside the marker's main gas chamber, which consequently keeps the velocity constant and more accurate. Markers equipped with a compressed air system and a good inline regulator can easily have velocity deviations of less than 2 fps, which translates to pinpoint accuracy at ranges below 60 feet.

Rate of Fire: From 0 to 60 bps in 20 Years

Paintballs are inherently inaccurate. Many have dimples that create turbulence and vortexes that cause them to curve away from the target. They are also very light weight, which makes them easily diverted by light winds, and when left in the heat, they swell and become deformed, further ruining their aerodynamic qualities. Because of this, your first shot probably will not strike its intended target, so it becomes vitally important to be able to fire a new paintball as quickly as possible. The desire to reach these higher rates of fire has driven the evolution of paintball makers.
The first paintball markers were hand-cocked, meaning the hammer and bolt had to be pulled back manually using a cocking rod. Hand-cocking was replaced by pump-action in 1983, which allowed players to keep their marker pointed in the general direction of their target while they reloaded [5]. In 1990, the muscle-driven pump was replaced by a ram-based pneumatic pump, a technological advancement that culminated in the first semiautomatic marker: the Autococker. The first blowback-based marker, which used excess gas to recock, was developed shortly thereafter, and in 1995 the first electronic markers emerged. The electronic markers, whose mouse-click triggers are as light as the buttons of a computer mouse, double players' effective rates of fire [5].
All major designs of mechanical markers share two common components that determine the marker's practical rate of fire: the trigger and the sear. While the trigger's function is easily understood, the sear is less obvious. The sear is a small lever controlled by the trigger that holds the hammer back. When the trigger is pulled, the sear is pivoted until it releases the lug on the hammer.
Although the blowback and autococker are designed to cycle at 20-40 bps (balls per second), the actual rate is limited by the force exerted on the trigger by the user. Usually only a little under a pound of pressure is needed for the trigger to trip the sear and release the hammer so the marker can fire, but this small amount is enough to severely limit a mechanical marker's practical rate of fire to only around 10 bps.
The development of electropneumatic markers was an attempt to lighten the trigger pull to allow for easier and faster shooting. Instead of using the finger's strength to trip the sear and release the hammer, an electropneumatic marker uses the strength of pressurized air to drive the hammer and in so doing reduces the sear to a small, microswitch [5]. As a result, the pressure that needs to be applied to the trigger to activate the firing cycle is reduced from the 16 oz previously necessary with mechanical triggers to as little as 1oz since all that is necessary is to trip the microswitch.
The development of the double-finger trigger, which allows players to pull the trigger with the pointer and middle fingers, introduced a new style of trigger-pulling. Termed "walking", this method involves tapping the trigger alternately with the pointer and middle fingers. It allows players to achieve rates of fire in excess of 20 bps on an electronic marker, an impossible feat using mechanical triggers [5].

Conclusion

"It's not the gun, it's the player behind the gun" is a common saying among veteran paintball players. While it is true that the game is more about a player's skill and daring than the price of his marker, it is equally evident that technological improvements have had a tremendous impact on the way the sport is played. These improvements have been aimed mostly at minimizing the technical problems paintball markers have had in the past (namely rate of fire and shot inaccuracy) but some improvements, such as the advent of electronically-contr​olled markers, were developed purely for the convenience of players. It is difficult to imagine other technological and engineering developments that could have such significant impacts on the game in the future because the innovations of the last decade have transformed the game from a weekend activity into a fast-paced sport with the attitude and style for mass-market appeal.

References

    • [1] S. S. Zumdahl and S. A. Zumdahl. Chemistry 5th Edition. Boston, MA: Houghton-Mifflin Custom Publishing, 2000.
    • [2] P. A. Tipler. Physics for Scientists and Engineers 4th Edition Extended Edition. New York City, NY: W.H. Freeman and Company, 1999.
    • [3] J. R. Little and C. F. Wong. Ultimate Guide to Paintball. Chicago, IL: Contemporary Books, 2001.
    • [4] J. Sparks, et al. "Viewloader Orion." Paintball Magazine Dec 2003: 58, 61.
    • [5] J. Braun, et al. The Complete Guide to Paintball. Hatherleigh Press: Long Island City, NY, 2003.
    • Janecka, Larry, et al. "Into the Breach." Paintball 2Xtremes Nov 2003: 133.
    • The PaintballGear.com Store. Oct. 24, 2003. http://www.pbgear.co​m.