Accuracy in Paintball - Part Three

Sometimes the difference between a hit and a miss is very small. Every little bit of improved accuracy can make a difference. Photo courtesy of Paintball Photography.

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Putting it all together.

Are you asleep yet?  I know this is a lot of technical information but bear with me because now we’re getting into the good stuff.  You have learned how physics work when it comes to a flying ball filled with paint, how the process for getting that ball moving works, and where in each part of that process the physics come into play.  However we haven’t talked about how these events, processes, and laws relate to the accuracy of your marker.  Well we will now.

Turning on the gas

Let’s start right where the whole process starts with the gas that gets the ball moving.  As we talked about gas uses both volume and pressure to move a paintball.  If either one of these variables change, the velocity of the paintball will also change.  Now if you remember from our last guide (and if you haven't read the last guide you should do so now) you recall that velocity has a big affect on accuracy and where the paintball will wind up striking the target. So let’s look at this image again:

Two paintballs fired from the same marker at the same angle and at the same elevation. The red line represents a paintball fired at a velocity of 300 feet per second (fps) and the green line represents a paintball fired at 200 fps. The heavy blue bar represents a target set at a fixed distance from the marker.

If you have a gas source that fluctuates in either volume or pressure you will have fluctuations in velocity.  So let’s say the red line represents a ball shot with a gas pressure of 324 psi and a volume of 8 cubic millimeters. (I really don’t know how they measure volume of a gas but the actual numbers are unimportant for the example) and the green line represents a shot with a gas pressure of 300 psi and a volume of 8 cubic millimeters OR a shot with a gas pressure of 324 psi and a volume of 6 cubic millimeters.

No matter what other forces come into play, the volume and pressure of the gas propelling the paintball are the start of the process.  Fluctuations here will result with fluctuations in the fps of the ball as it leaves the barrel.  This is why the first step in making a paintball marker accurate is to get the amount and pressure of air delivered with each shot as consistent as possible.

This is done through air regulation and valve control.  Air regulation will stabilize the pressure of the gas being delivered to the valve and keep it consistent from one shot to the next. Controlling the valve will control the volume of air delivered to the bolt with each shot.  Let’s go over these two items in a little more detail.

  • A regulator like this Palmers stabilizer is a must have when it comes to having an accurate marker. HPA tanks come pre-regulated while CO2 tanks require a regulator to be added to the system.
    Regulation – Both CO2 and HPA can be regulated.  Since HPA is stored under very high pressures (3000-5000 psi) the bottles come with a regulator installed that will reduce the output pressures to a level paintball markers can use.  However, CO2 as a gas source is tricky. You see, CO2 is stored as a liquid, not a gas like HPA.  Thus to use it we must first have it change from a liquid to a gas.  CO2 requires heat and room to do this.  If you increase the area that you are using to store the CO2, more of the liquid CO2 can turn into a gas at a given temperature.  If you increase the temperature of the container, more liquid CO2 will expand into a gas as well.  This means that a cold CO2 bottle will have less gas and thus a lower output pressure than a hot CO2 bottle.  This pressure difference can be very large with a cold CO2 bottle putting out 300 psi and a hot bottle putting out over 1200 psi!  This is why a marker running on CO2 may shoot at 285 in the morning when it’s cool but be at 360 in the afternoon when it has gotten very hot out.  By adding a regulator (or two) to a CO2 system, this output pressure can be regulated so that it stays constant.  However, in cold weather conditions the output pressure of CO2 can drop to a level below what the marker can operate on.  This is why HPA is a better choice for cold weather climates.  Also, in rapid fire conditions, more liquid CO2 is converted into gas with every shot.  This conversion takes heat to accomplish and this heat comes from the air surrounding the bottle.  Thus the more you shoot the colder the bottle gets and the less heat there is in the air surrounding it resulting in less and less liquid being converted to gas with each shot.  This lowers the output pressure and again can result in the pressure dropping so low that the marker will not operate.  Again, this makes HPA a better choice over CO2 when it comes to rapid firing markers and their accuracy. 

This means if you take two identical markers and run one on unregulated CO2 and the other on HPA, the HPA marker will SEEM more accurate only because it is getting consistently regulated air.  Most high end markers require the use of HPA because of their delicate valve systems and this leads many new users to feel that these markers are “more accurate” than their older CO2 powered markers. 

Also, if you must use CO2 it is highly suggested to try and lower the operating pressure of your marker.  This will make your marker less susceptible to problems and issues associated with low CO2 pressures because of low temperatures or high rate of fire conditions.  

  • Valve Control – Valve control is something that most people do not think about.  Basically the further a valve opens and the longer it stays open the greater the volume of air it releases into the bolt to fire the paintball. Again, remembering back to our talk about pressure and volume affecting velocity, when you adjust a velocity adjustment screw on a Spyder style marker, what you are doing is increasing the force applied to the spring that pushes the striker into the valve.   The harder this striker hits the valve, the longer the valve stays open, the more air that gets to the bolt and thus the higher the paintball’s velocity.  Usually this is about the only control we have over the valve.  However, with the newer electro-pneumatic markers users can program how far and how long the solenoids that control airflow open. In general, electro-pneumatic markers are far more consistent with how much air they deliver than more mechanical markers.  This is not to say there are not things a user can do to a mechanical marker to increase its consistency.  Polishing the striker and eliminating as much friction between the striker and the body and replacing worn out springs and o-rings will help keep the marker firing as consistent as possible.

Again, and I cannot stress this enough, having the pressure and volume of your gas under control is the first and one of the most important items when it comes to having an accurate marker.

Paintballs

Next let’s talk about the rounds.  They are, after all, what we want to hit our target with and because of this play a big role in how accurate our shots can be.  There are three things that we want to look at when talking about paintballs:

  • Size – Paintballs are never the same size even if they are the same type out of the same case.  However, some brands are better than others. 

  • Roundness – No paintball is perfectly round.  I’ve seen some that were so bad they looked like an egg.  Like with size though, there are brands that are closer to being perfectly round than others.

  • Smoothness – The two big things here are seams and dimples.  Storage and age are the biggest factors when it comes to dimples but these can be easily checked for when purchasing your paint.  Seam size though will vary from brand to brand.
Getting a good paint-to-barrel match means making sure the paintballs you shoot fit the bore of your barrel properly. But no matter how well that match, a dirty barrel like this one will cause your balls to fly wildly. Remember to always clean your marker for best performance! Photo courtesy of Paintball Photography.

Why are these three things so important? 

Most of you may have heard about making sure your paint has a good “Paint-to-Barrel” match.  What this means is that the paint “fits” in your barrel.  To test this, you place a paintball in the back of the barrel with the barrel pointed down.  The ball should stay in place.  You then blow on the back of the barrel gently and the paintball should get blown out of the barrel.  If the ball rolls out of the barrel, the ball is too small.  If it takes more than just a gentle blow on the back of the barrel to dislodge the paintball, the paintball is too big.  That’s the simple explanation. 

By having the ball fit just right in the barrel, the paintball will “seal” against the barrel making an airtight chamber between the ball and the bolt when the air charge is delivered.  This is the most efficient way to fire a paintball as every bit of energy in the air charge is used to accelerate the round.  If the ball is too small, gas can escape past the ball and be wasted.  If the ball is too big, the amount of friction between the ball and the barrel wall will increase and more energy from the air charge will need to be used to overcome this friction.  In either case, the velocity of the ball will be less than it would be if the ball fit in the barrel properly.

Importance of Size
However, not all balls are created equal and some are smaller than others even if they both come from the same case of paint.  So just because one ball out of a case passes the test does not mean all of them will.  Because of this it is important to buy paint that has a “size range” that averages what the bore size of your barrel happens to be and has the smallest “margin of error” as possible.

To determine your barrel’s bore size, find a paintball that passes the Paint-to-Barrel test perfectly. Now measure the size of that ball using a ball sizer or a good set of digital calipers.  This now gives you the average you are looking for.  Let’s say the number is .690.  Now you will want to measure a good sampling of balls from the case and write down the size of each one.  Say you measure 50 balls. (Out of a case I might consider doing 200…or 10%)  Add up all the measurements and divide the result by the number of balls measured…50 in this example. This will give you the average size of the balls in this case. 

Now the other factor, “Size Range”, is a little bit trickier.  You want to divide your measurements now to those balls that were smaller than average, those that were exactly the average size, and those that were larger than average.  The more balls you have in the “exactly average” size the better but we’re looking at the other two groups.  They should be fairly close to even.  Now look at the smallest and largest size balls you measured.  If the groups are close to even these two numbers will give you your “Size Range”.  The closer these numbers are together the better.

Here’s why.  Let’s say you have a bore of .690 on your barrel and two cases of paint both of which have an average bore size of .690.  However, one case has a size range of .688 to .692 and the other has a size range of .689 to .691.  This latter case will be more accurate from shot to shot because the balls are all closer to the ideal size of .690 than the former case. 

When you have paintballs with consistant size, roundness, and smoothness these are the results. Now THAT'S accuracy! Photo courtesy of Paintball Photography.

Importance of Roundness
Having all the balls as close as possible to the ideal size is only one part though.  Paintballs are not only inconsistent in size but in shape as well.  Some paintballs are almost perfectly round while others can be shaped like an egg.  As with size, shape also tends to affect accuracy.  First off, a ball that isn’t perfectly round will have high and low spots.  This will mean that while part of it will make a nice seal with the barrel other parts will leave gaps between the ball and barrel allowing the air charge to partially bypass the ball.  Not only that, but when flying through the air the odd shape will mean that vortices will form unevenly during flight and cause erratic flight patterns. 

A ball sizer can be a big help in determining not only ball size but roundness as well.  Take the same sample of balls you used for measure size and put them through the ball sizer again.  This time though, rotate them in the holes of the ball sizer.  You may notice that sometimes they rotate very easily and other times they will “stick” when certain parts of the ball are moved through the sizer.  This “stick” tells you the ball is not perfectly round.  The smoother the ball rotates in the hole of the sizer the closer to perfectly round it is. If most of the balls pass this test, the case paint is said to be of “uniform roundness” and will shoot more consistently from shot to shot.  

Importance of Smoothness
So now we know the balls are of a consistent size and uniform roundness what about how smooth the surface of the ball is?  There are two major items that affect the smoothness of a paintball, its seams and dimples.  Seems are where the two halves of the paintball shell are joined during the manufacturing process.  On high quality paintballs, these seams are usually very minor and shallow.  Running one’s finger across them may not even be able to detect them.  This is a good thing as the deeper the seam the more air they will catch during flight.  When a seam catches the air, it will form stronger vortices than if the air were passing over a smooth part of the paintball and thus the ball will be more likely to fly off course.  The good news about seams is that they tend to be pretty consistent throughout a case of paint.  Checking a handful of balls usually is enough to determine if a type of paint has good seams or not. 

Dimples are another matter.  Dimples are caused by paintballs sitting for too long without being rotated.  The constant weight of the paintballs at the top of the case pressing down on the paintballs in the bottom of the case for long periods of time will cause the areas where the paintballs touch to flatten out.  These flat spots are called dimples.  Like seams, dimples will cause undesired and more powerful vortices to form on the surface of the paintball where they are located.  Heavily dimpled paintballs are known to fly wildly off course and not come within yards of their intended targets.  Inspecting your case of paint BEFORE you buy for dimples can save a lot of trouble later on.  You should be inspecting for broken balls in the bags of paint anyway so add checking for dimples to your paint buying routine.

Barrels

We’ve covered gas and we’ve covered paintballs but without a barrel no marker will be accurate. Believe it or not, the barrel is the least critical of the three when it comes to having an accurate marker.  This isn’t to say it has no role in accuracy, but too many people put a lot of faith into barrel upgrades as a way to increase the accuracy of their marker. 

A good, high quality barrel is important to having an accurate marker but it certainly isn't the only thing.

The first thing that a barrel does is form a seal with the paintball to allow the air charge to use all of its energy in accelerating the paintball.  This isn’t totally true though.  When the paintball is fired, friction will be generated where the barrel touches the paintball.  As the speed of the paintball increases, the amount of friction generated increases.  This means that even if none of the air charge bypasses the ball some of its energy will still be “wasted” in overcoming the force of friction as we mentioned earlier.

By choosing a barrel that is smoother and more consistent in diameter down its bore this friction force is more predictable and linear making for more accurate shots.  However, even when comparing barrels at either extreme, the differences are less significant than that of gas regulation or quality paint.

The barrel will also direct the ball towards the target.  After the first 8 inches the next two to six inches will help allow the fill in the ball to stabilize from the rapid acceleration following the delivery of the air charge. How much this extra “stabilization area” benefits accuracy is, like many items, debatable.  It has been generally accepted that the ideal length of a barrel is longer than 8 inches but no longer than 14 inches and that additional barrel lengths beyond 14 inches do not provide any benefit to either accuracy or range. 

“Flatline” Effect and Riffling
There are two classes of barrel that do offer some benefits due to their design over other barrels however.  These are the “Magnus Effect” barrels and the “Rifled” barrels. 

The Tippmann Flatline, the APEX, and the Warsensor Hop Up Barrel all will impart a backspin on a paintball and allow it to fly further with a flatter trajectory than other barrels and are considered “Magnus Effect” barrels.  However, this benefit comes with a price.

A Tippmann A5 with the Flatline barrel. While the improved range and flat tragectory this barrel provides can be enticing, it comes with a price. Don't expect the best accuracy from this barrel especially at those longer ranges. Photo courtesy of Paintball Photography.

With the Flatline, the barrel is not straight.  Rather the barrel looks “bent” upwards.  When the ball leaves the breach it is forced upwards against the top of the barrel by this curve.  In addition, the inner bore of the barrel is rough rather than smooth to increase the force of friction between the ball and the barrel.  These two modifications impart a backspin on the ball to have it benefit from the Magnus Effect.  With the Flatline, the ball must be slightly smaller than the barrel bore to allow it to spin freely when it comes in contact with the top of the barrel.  Because of the curve, the added friction, and the smaller ball requirement, Tippmann Flatline equipped markers will generally use more air to achieve the same velocity as a normal barrel equipped marker of the same make.  This is offset some by the fact that the Magnus Effect produced by a Flatline barrel is optimal when the ball is fired at 270 fps which is under the normal 285 fps that most fields set as their maximum allowable velocity.  

The Flatline has been shown to be significantly less accurate as standard barrels and to this date no one has come forth with any study that determines why this may be.  Personally I feel the rough surface of the bore coupled with the way the barrel is curved produces unpredictable gyroscopic effects. 

The APEX and Warsensor barrels both apply the Magnus Effect back spin using straight barrels but do so in much different ways.  The APEX uses a special tip that is affixed to the end of the barrel.  Inside this tip is a rough pad that will brush the top of the paintball as it passes through the tip. This increases the amount of friction against the top of the ball to impart the back spin.  Because a tight paint to barrel match can be maintained through much of the ball’s travel down the barrel the APEX system tends to be more accurate than a Flatline system.

The Warsensor Hop Up barrels use yet another method to impart back spin.  Located at the top of the barrel’s bore are three groves at roughly 11, 12, and 1 O’clock positions running the entire length of the barrel.  These three groves allow some air to bypass the top of the ball thus reducing the amount of air pressure on the top of the ball.  This forces the ball up against the groves and the friction of the ball against these groves imparts the back spin.  Because air pressure is more consistent regardless of ball size the Warsensor barrel is more accurate than the Flatline system and produces similar range benefits.

The last type of improved barrel systems is the riffled barrel system.  It is still a matter of debate as to how much these barrels increase accuracy if they do anything at all.  While early riffling tried to impart a spiral type spin on the paintball to give it gyroscopic stabilization like a real bullet, the liquid fill inside the shell would not spin at the same rate as the shell and tended to “slosh” around inside the shell making the riffling useless.  However, the new Tippmann/Hammerhead riffled barrels seem to rely more on trying to equalize the pressure of the air charge against the ball by directing it through the riffling and thus producing more accurate shots.  Warsensor had a similar barrel that used straight porting on all sides rather than spiral porting to achieve the same effect but the barrel was produced in such limited number as a real world collaboration of the effectiveness of the barrel was inconclusive. 

Again, it should be noted that these riffled barrels are the subject of much debate.

Closed bolt, long barrels, recoil, and myths to accuracy

Some will say that a closed bolt marker is more accurate than an open bolt marker or that a longer barrel provides a more accurate shot.  These and other myths have a bit of truth to them but they are not completely true statements.  When it comes to whether or not a particular marker design will affect accuracy it comes down to something called recoil.

Some believe that closed bolt markers like Autocockers or this Phantom pump are inherently more accurate. While the debate will probably never end studies have shown that there is very little difference between open and closed bolt markers. Marker recoil plays a larger part in shot to shot consistancy and accuracy. Photo courtesy of Paintball Photography.

Good old Newton had one more “Law” up his sleeve when the apple popped him on the head.  His third law states that for every action there is an equal and opposite reaction.  In paintball, the action is firing the paintball…the reaction is the recoil of the marker as it resets for the next shot.  Now Physics students who are reading this are going to give me grief because this isn’t a true “action/reaction” scenario but it’s close enough for this example. 

Recoil is that force you feel when the gun kicks back in your hand after you pull the trigger.  On come markers, it’s very slight and on others it’s pretty hard.  Generally, the harder the recoil the more likely the paintball may be affected as it travels down the barrel…or more appropriately where your barrel is ACTUALLY pointing when the paintball leaves the barrel in comparison to where you had it pointing when you pulled the trigger.   Recoil is also a compounding factor meaning the faster you are shooting the more recoil affects your accuracy and it increases its effect the longer you shoot.  This means if you take one shot recoil will affect your shot very little if at all. However, if you take the next shot shortly after the first without allowing the marker to reset after the first shot and readjusting your aim after it resets then the second shot is less likely to hit the target the first shot was aimed at.  This factor increases the faster you shoot and the more balls you shoot at that faster pace. 

This means a marker with LESS recoil will have better accuracy when firing multiple shots at high rates of fire but when it comes to single shots it will be no more and no less accurate than any other marker shooting with the same paint/barrel/air source combination while chronographed at the same velocity.

It used to be believed that closed bolts offered an accuracy advantage over open bolt markers because the bolt fired the ball with the bolt already forward and in the “ready” position.  With an open bolt marker, once the trigger is pulled the bolt must slide forward and then fire the paintball.  There may be some truth to this as, on single shots, closed bolt markers such as pumps and cockers seem to display astounding accuracy.  Again though, once the operator begins firing multiple rounds at high rates of fire such as with an eCocker, accuracy tends to be the same for open and closed bolt markers.

While they may look cool, barrels longer than 14" do not make a difference in the accuracy of your marker nor do they add any distance to your shot. Photo courtesy of Paintball Photography.

Lastly, for a long time it was believed longer barrels meant more accurate shots.  This was derived from the first days of paintball when many markers had barrels under 8” in length.  It was found that when these barrels were lengthened to between 10 and 14 inches that their accuracy improved considerably.  This was mainly due to the fact that the ball now had a full 8” to accelerate and another 2” to 6” to stabilize before leaving the barrel.  Today, most markers already come with barrels that fall between these two lengths.  However, the old idea that “longer is better” has hung around and have led many to believe that replacing their 14” barrel with a 20” “Sniper” barrel will increase their marker’s accuracy.  While there may be some improvement if the short barrel is of poor quality and the longer barrel is of much higher quality, the increase in accuracy will be due to this quality difference and not the overall length of the barrel.

In the Simplest of terms…

There is a lot here, I know.  Believe it or not, there is a lot more to all this than what is here and going over it all might confuse more than clarify.  The just of this article is pretty straightforward.  Due to what we call physics, the humble paintball can only be fired with a finite degree of “accuracy”.  They can only be so good.  The pressure and amount of gas used to propel the paintball, the size, roundness, and smoothness of the ball itself, how well the ball fits the barrel, and the smoothness and straightness of that barrel’s bore all contribute to the overall accuracy of the marker.  If all those issues are addressed and controlled as much as they possibly can be under the current “reality” of paintball the marker will be as accurate as paintball will allow.  Length of barrel, closed or open bolt, and the overall design of the marker make little to no difference to the accuracy level of the marker.

Most of the time in this sport the targets we have to shoot at are small. Someone's head peaking out from behind cover, a foot sticking out from a bunker, the top of a hopper sticking up just a little above a log. Improving your marker's accuracy will result in you making those shots more often. Like this series of pictures show, the difference between hitting your target and missing it completely can be measured in millimeters. Note in the left picture the orange "pill" by the player's barrel is the incoming paintball. Photos courtesy of Paintball Photography.

Conclusion

So there you have it.  This is by no means the end all be all of paintball accuracy.  Theories abound and opinions are like…well…they’re everywhere.  This guide only scratches the surface of the physics and theories that are behind paintball accuracy.  Most of what is here I’ve compiled from a number of different topics on the subject.  If you would like more in depth information about how and why this all works, please visit some of the following sites:

Armorer’s Paintball Ballistics Thread on Ariakon.com
(Wouldn't you know it. The forum goes down just after I wrote this. I will leave this link here just in case they get it back up and running.)

The Physics of Paintball by Gary Dyrkacz

The Official Data thread from the Air Gun Designs (AGD) forums.

Paintball Spin Physics – Getting to the final Answer on the AGD forums.

Good luck and remember, it is all about having fun!

- Robotech

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