Things to ponder with how much pressure you need.

[CHK6]

In my learning I questioned what is the lowest pressure need to propell a paintball to 280 fps in 10 inches? Now granted this is the inital baby-step in coming up with a more complex answer. So imagine a system that is open at one end for the paintball to leave and a the PSI level that is constant through acceleration. I haven't figured in friction of gelatin on aluminum/steel/brass. If you happen to know the frction coefficient (u) of gelatin on one of these combinations I would appreciate it if you let me know. I just don't happen to have a block of gelatin and aluminum handy. If I did it's a simple test to gather the friction number.

Onto the fun stuff..... *Note: all numbers are in metric.

Time
t = 0.254000508001 / 85.3444 = 0.002976196 seconds for the ball to travel 10 inches and peak at 280 fps.

Acceleration
a = 85.344 / 0.002976196 = 28675.53078 m/s^2 acceleration for 10 inches

Force
F = 0.003188 * 28675.53078 = 91.41759212 newtons

Area
A = 4(PI)(r^2) / 2 = 0.000468603 m^2 ; this is area (standard .68 ball)

Pressure
P = 91.41759212 / 0.000468603 = 195085.3753 pascals

195085.3753 pascals = 28.294743 PSI

If this is correct, then this is extremely interesting. If I'm correct we can't supply a constant flow of ~28 PSI for 10 inches against an area of 0.000468603 m^2 for 0.002976196 seconds. So the next thing to figure in the PSI volume expansion ratio. That should bump this up to ~100 psi.

[AGD]

Nice job! Looks about right too! Yes somewhere around 28 psi will get the ball going in 10 inches. The problem is you waste the rest of the pressure out the end of the barrel after the ball leaves. empty barrel + 28 psi = wasted energy and low efficiency.

To get best efficiency you need to start with "x" psi and use it all in 10 inches but still get the ball to 280 fps.

For example start with 80 end up with 10 when the ball leaves gives you an average of 35 psi accelerating the ball.

Do some math, I'll monitor the post.

AGD

[Puddleglum]

Wow (you can take this post out if you feel it doesn't belong) That is really impressive. I thought algebra was tough. Keep up the good work.

[Vegeta]

Well, you cant have porting anywhere in that barrel, you know that. And it also depends on hte surface of the barrel, and like you said you couldn't find the friction coefficient. But, problem is, if hte user of this "super-low pressure gun" changes barrels, say, from a creamic to a hoed aluminum, then the pressure will have to go up/down, depending on the switch. Paint travels over certain sufaces much easier than others. But you see this on all guns, so no biggie.

Another I dea is, using an ultra-low pres. gun with a lubed barrel/ ball. I would think you could use lower pressure if hte ball or barrel was lubed to an extent. You barrel would have to be coated evenly (or turbulance could result on the ball), and be about 0.002 bigger than the ball to allow for the thickness of the bit of oil. Then you should be able to drop that psi from your already low 100 or so PSI to about 60. Im not sure how these barrels would be lubed, either by oil, which is rather primitive, or by new, ultraslick materials. Problem with oils is that it rubs off, and onto the ball, cuasing air turbulance, which cuases inaccuracy.

Ultra low psi would mean great things for paintball. more shots per tank.. less money. Of course, fill stations would raise prices most likely becuase of the loss of business due to ppl not coming in as often.

Just some thoughts...

[CHK6]

I wouldn't say integretion is my strongest subject, but I do know how to. Integrating over time, PSI, and distance isn't a small task for me. I guess I should have paid more attention in the later parts of calculus II class.

Luckily I picked up some "light" reading. "Fluid Mechanics" by Merle Potter and John Foss. Right now I'm still on chapter 1 and I feel like the Lawn Mower Man in the amount of information each page holds. Eventually I'll hit paydirt in later chapters that talk about compressible fuilds.

Baby steps...and building blocks...no task is to difficult. Eventually, I will hopefully be able to create the building blocks of a Java API paintball simulator; where all paintball markers can be modeled and tested under virtually.

[fenris69]

I haven't seem any specs on this yet, but the new 'Lunacy' from splatmaxx section8 is quoted at 25psi operating pressure. Seeing as the original Nova did 90psi no problem this could be interesting.

[pbjosh]

Well,

I have gone off about this topic more than once on other forums, but here it goes.

What is being looked for is not pressure/velocity but ENERGY/velocity.

A mag has about .55 ci chamber with a 400+ input pressure.

So the energy usage is about 220 in3*lbs of energy.

A shocker uses a chamber of 1.8 ci with about 180+ psi input.

So the energy usage is about 324 in3*lbs or better.

Now a tank of 68 ci in size, at 3000 psi is storing about 204,000 in3*lbs of energy. If the gun runs down to 400 psi, then the last 68ci at 400psi can't be used.

Get the picture?

Here is more. If you take the total area used by a dump chamber gun, like a 'Mag or Shocker, from the point that the ball is 10" down the barrel, and include the volume for the dump chamber and the bolt/powertube/valving arrangement, you get a total static pressure of about 40-45 psi.

A Shocker and Matrix are both very in-efficient. Both have very large volumes between the dump chamber and the bolt head. Both have huge dump chambers.

A Mag has a small dump chamber and small bolt/powertube volume.

Hence the effecientcy.

Enjoy,

Josh

[steveg]

Hey pbjosh afraid that I'm going to have to throw a monkey
wrench into your theory, the matrix is inefficient in stock
form because it wastes gas with every shot. The aarvdvark
bolt kit removes this waste and allows the matrix to use
the gas effectively. most users are experiencing about
800 shoots per 68/3000, much the same as a mag.
Oh well back to the drawing board.

[pbjosh]

I have never really had a chance to measure the internals of a Matrix, so I don't know the volume.

And, I have a design that is a dump chamber, and right now I am running at les than 200 ci*lbs of energy each shot, putting it below a stock angel.

Here are a couple of things I posted on another site:


The basics for the gun and tank are this:

We are looking for VOLUME * PRESSURE = ENERGY.

Energy is the amount of air used, at a certain pressure, and a certain volume. The more Energy used, the less efficient the gun. Easy.

Now look at this. A tank has a fixed amount of air, or volume, and that volume is charged to a certain pressure. Say we have a 68/3000 psi tank, charged all the way. We multiply the volume with the pressure to get 204,000 in3*lbs of potential energy in the tank. If a gun runs the tank down to 400 psi, then they don’t use the last 27,200 in3*lbs of energy in the tank. So you get 176,800 in3*lbs of energy used. If you figure out the guns number of shots from 3000 psi down to 400, then divide 176,800 by the number of shots fired, and you get the amount of energy used in each shot.

So, just figure out how many shots per tank, and the tank size, you get the energy used by each gun.

I did this to figure out the volume needed to build the Shiva. I also figured out some other stuff, but that will come later.

I did figure out the that fixed volume guns, like the ‘Mag, could give a good number for the amount of air used because they have the volume and pressure measurable for each shot. A ‘Mag has about .55 ci of volume in the dump chamber, which is ran at about 400+ psi. I figured the gun uses about 210-225 in3*lbs of energy in each shot. A Shocker, which has about 1.8 ci of volume, and runs at 180 psi+, we can figure out that the Shocker uses about 324 in3*lbs of energy. And, from what I have back figured from amount of shots fired per tank, the Shocker can use over 365 in3*lbs per shot on a consistent basis. A Matrix uses about 310 in3*lbs of energy, and the average blowback uses about 270 in3*lbs of energy.

Now, I need to get new good number figured out for the Shiva, but I am running less than 200 in3*lbs of energy used. And that is without the best paint to barrel match.

If a person takes an Autococker (or whatever), and takes an accurate pressure reading, then fires a couple of hundred shots, with their paint and barrel, and record the average velocity, and the pressure drop, they would get a VERY accurate reading of the energy used by that gun, with that barrel, and that paint. The only hard part is finding a high quality pressure gauge. So, if you want to figure out how efficient your gun is, there is the guide.

Fill up your tank, get a GOOD gauge, fire a couple of hundred rounds, and you have the amount of energy used. SIMPLE.

All the “pressure to get what velocity” questions are just a crock of dookie. What they are wanting to ask is the amount of energy used. And now you have a way to find it.


I consider the wrench removed.

Your turn

Your home work is to tell me what tank you have, what gun you have (barrel and all that) and what ever else. THEN give me a number for amount of you get and the amount of air you use. I can then average the amount of air used per shot for you guys, and we can figure out how truly efficient each gun is. Just as long as everybody is honest, and does try to count the amount of shots taken, then we can get good numbers. Accurate counts, and honest pressure.

Full report due this weekend

Josh

[steveg]

OUCH you throw a mean gauntlet there pb;)
I will supply the dump chamber volume for a (my) matrix soon

as for accurate gauges try here http://www.winters.ca/pre_process.html

I bought a 0-300psi 1 1/4" gauge from one of their dealers
for C$ 11.00

[pbjosh]

oh, I already have the gauges, and they are 0-200 and industrial, for use with the 'Shiva'.

And for everybody reading this post, please attach your numbers, for tank size and pressure, plus type of gun. A chart of some such that tells the number of shots per gun and the size of the tank can be produced from that. Let me make some other posts for this so I can get a average number of shots per tank per gun, and then I can post some good numbers for the energy usage of several guns

Later,

Josh

[steveg]

Back again The volume of a matrix dump chamber is
21.5 ml (measured with graduated syringe) or 1.312 cubic in

A handy link for the conversion challenged http://www.onlineconversion.com/

[pbjosh]

VERY NICE! you figured it out with a syringe! smart.

Okay, the matrix does still dump some air, right?

and run at 140 psi?

the 140psi * 1.3ci = 182 in3*lbs which is VERY GOOD.

So, where does the rest of the air go. Some one had built a paintball gun that shot as much air out the back of the gun as shot air out the front of the gun! HAHAHAHAHAHAHA! oh boy, that seems really silly.

LOL- that still gets me.....

Josh

hehehehe

how many shots from a tank do you still get?

Humrph....hehe...giggle....

[steveg]

actually it takes about 180 psi for 280 fps I have to confirm this as It's been about a month since I've last
played:eek: so 180psi * 1.3ci = 234 in3*lbs

still not bad

further 204000 in3*lbs/234 in3*lbs =872 shots

That number is of course "ideal" so what happens in real life is different.

As for shots per tank I confess that I haven't had the bolt kit long enough to personally confirm or deny 800
shots, 68/3000 It is what people at pbnation are claiming that they are experiencing. plus I have to use a
scuba tank so I never get a real 3000psi fill.

None the less my original post was to warn you of an incorrect
assumption as to why the stock matrix got lousy
gas mileage. There are no elves involved in the arrdvark bolt
kit merely the correction of a design mistake that allowed
air to be wasted on the return stroke of the bolt
(by chance did you already know this?)

OH and how about some links to those "other" sites

[pbjosh]

As to other sites,

Actully, I have written almost the same thing to most of the other sites out there. I usually hit the Tinker's guild and the pbnation. I just put a survey up in pbnation paintball talk asking for shots per tank adn all that. chaeck it out. And on pbnation in the paintball news section is the 'Shiva' project.

The 'Shiva' is mine.

Josh

[CHK6]

Wow, I read all the above posts. Interesting.

I think I'm on the right track in figuring out pressure loss in piping, but I need to figure out how to calculate SCFM.

Most problems explain what SCFM is and give it a value to calculate ICFM, but never states how one derives SCFM.

Anyone know how to do this?

UPDATE: Never mind I figured it out and have a completed formula. All I need is a couple of reference tables for relating density to temperature and some others.

[pbjosh]

okay everybody,

I did a quick survey on pbnation, and i guess I will post one here soon.

Here is an energy used chart, per gun.

Now, these are not tested numbers, but from a list of peoples postings about which gun, how many shots, and what tank. So, error is included. Just for now, this is just a beginning. I want to fill this up to the point that we can figure out valves and barrel ratios also.

So, if you read this, post something like....

I have a SFL Snagler ACE with an 68/4500 tank and I get 900 shots per tank @ 225 psi

Thanks,

Josh

[CHK6]

PBJosh,

The energy the tank holds also heavily depends on local barometric pressure, temperature, and altitude above sea level.

I have also found some other interesting tidbit relating to PSI levels. When talking "shop talk" I found that you either have to say PSIA or PSIG and just saying PSI will get you funny looks from individuals that work with compressed air. And if you say what the PSIG is you have to give the local barometric pressure.

I also found out that the barrel id has an effect of how many shots you get with the energy in a bottle.

Also when calculating pressure temperature you have to convert Farenheit to Rankine. Something I wasn't doing and really scewed my results.

Just sharing the information I have found in better hopes to truely understand it all myself.

Later gator.

[pbjosh]

Well, it all gets down to averages. A person can tell me how much pressure is in their tank, but the gauges on a tank is not to accurate. Also I will get basic averages for the number a shots per tank, generally rounded off to 50 or 100.

Barrel has alot to do with it, but the general average for the gun will be a bigger factor. And part of this is to educate. The amount of energy used per gun on average is a number nobdoy uses to figure out efficinct, but should be incorporated in everybodies ideals for how a gun works. How many people think that low pressure means high efficiency? With a basic graph, this should help people realize what gun they want, but also what tank. If a person thinks that one valve is better just because of its working pressure, then they are not taking into account the amount of energy used per shot.

A different bolt, or even operating pressure can affect all of this also.

Again with the accuratecy of a post to a survey, and the gauges, and everything else, the difference for the local barometric pressure temp, and PSIG and all that, it doesn't really matter. I am dealing with larger numbers and averages than that. And the reason for a large # of averages is to sort that information outta the mix. I don't want an effecientcy number based on a certain air pressure, certain paint, certain barrel. I want an average for that gun, in any local barometric pressure, at any temp, and etc.

So, tell us, how many shots from what gun and the tank you use at what pressure and what velocity.?

Josh

[AGD]

Pbj,

Nice data table!! Glad to see someone wants the facts. I agree with you that a large sample size will average out the variables. I would like to see the formulas you used to get the energy in the tank and the per shot energy.

Thanks

AGD

[CHK6]

To answer the question I get 250 to 300 shots on any given day with 3.5 oz CO2 on my Phantom. Pressure ranges from 800 to 1000 on the guage.

[pbjosh]

AGD! proud to have you on this!

Okay, here is all I did to figure out the numbers.

I originally posted over a 2 years ago on the tinker's guild to a question about the pressure it takes to get the ball to 300 fps, like on this post. I was posting on how the number that they are looking for is a value of energy, not pressure.

Then I collected the numbers for the volume of a couple of guns with fixed chamber dump valves. Since energy is a measure of Volume x Pressure, I figured I could get the right numbers from multiplying the Volume of the dump valve with the pressure the gun ran. And, then I smacked my head and said "Hey, all the guns have a fixed amount of energy attached to them! The HPA tank!"

So in the basic 68/3000 tank, multiplied, you get 204,000 ci*lbs of energy in the tank! And if a gun runs till 400 psi, a person would take the volume of the tank, minus the amount of air unused, like 68 ci x 400 psi = 27,200. So, 204,000 - 27,200 = 176,800. And if a gun gets 800 shots, then divide the energy that can be used, 176,800, buy the number of shots, 800, you get the energy used, so:

176,800 / 800 = 221 ci*lbs of energy on each shot.

I just asked about the gun, the tank size and the number of shots @ which pressure. That gave me the total energy used per system. So, even if it doesn't have the exact amount of air used down the barrel, it does give a relative number for the energy used per gun. And I must say, the 'Mags are the best dump shamber out there right now, with 200-225 ci*lbs of energy used. A gun like the Shocker is horrid, with 365-400 ci*lbs common.

Well, that about it, just whiped up an Excel file and that was that.

Now go my children, and spread the word.

Josh

[athomas]

Lets get more elaborate here. I'm no expert at math anymore, its been a few years since I've picked up a math book, but I am interested in some of the dynamics here.

for ease of calculation:

Mag chamber pressure = 400 psi
translates to 220 in-lb of work force

Actual force on the paintball at start is 150lbs when properly vectored, as it is the cross sectional area of the ball that is important, not half of the surface area. 150lbs represents the pressure in one direction(out the barrel).

Chamber = .55 ci
cu area of 1 inch of barrel (id = .690) = .3739 ci

Lets plot the acceleration force of the expanded gas.

distance = force
start(0) = 150 lbs
1 in = 89 lbs
2 in = 63.4 lbs
3 in = 49.2 lbs
4 in = 40.2 lbs
5 in = 34 lbs
6 in = 29.4 lbs
7 in = 26 lbs
8 in = 23.2 lbs
9 in = 21 lbs
10 in = 19.2 lbs

As you can see, the amount of force on the ball decreases as the gas expands and the ball accelerates down the barrel. Therefore the rate of acceleration is not going to be standard. Most acceleration is calculated using a constant force.


Now, I can't find my books with all my formulas, so I need your help here. Can anyone figure out a formula for calculating the actual rate of acceleration of a paintball down the barrel of a paintball gun. If we can come up with a standard formula taking into account the changing volume of the chamber-barrel as the ball accelerates it will help us realize the benefits of changing pressures, volumes and barrel lengths.

I did some quick calculations and noted by eye that the effect of doubling the chamber size and decreasing the chamber pressure doesn't work. It is more like double the chamber size, decrease the pressure by 25%. The amount of in-lbs of useable gas increased. In the other direction we could greatly increase the efficiency by increasing the pressure and decreasing the chamber size. The starting force would be increased and would probably cause the balls to explode in the gun though.

I know my data has gaps in it but the fundamental concept is basically sound.

Hope this helps.

We can do it for the betterment of mankind on the painball field.

[bjjb99]

Fair warning, I'm going metric on you guys. That being said, here
we go...

First off, some basic formulas.

1: F = m a
2: F = P A
3: P1 * V1 = P0 * V0

Notes:

Formula 1 is your basic "force equals mass times acceleration"
equation. Formula 2 relates force, pressure, and area. Formula 3
describes how pressure and volume interrelate. The "*" symbols in
Formula 3 are multiplication symbols, for those who are used to
seeing "x" instead.

Since we're interested in the acceleration of the ball at any
point in a barrel, we really want to solve Formula 1 in terms
of the variable "a".

a = F / m

Now, we have a pretty good idea what the mass of a paintball is
(around 0.116 ounces, or around 0.0033 kilograms). What we need
to know is how the force on the ball varies as the ball travels
down the barrel. This is where the second formula comes into
play.

The force on the ball as a result of the gas behind it is
dependent on the pressure of that gas and the cross-sectional
area of the paintball.

F = P A

We can calculate the cross-sectional area easily enough. A
paintball is right around 0.68 inches in diameter (0.017 meters).
Area is simply Pi R squared, which gives a final area of
0.00023 square meters. Why am I using square meters for something
so tiny? Because the pressure values I'm going to be using are
expressed in units of force per square meter of area. So now
we have the following for Formula 2:

F = 0.00023 P

We can plug this into our acceleration solution for Formula 1 to
get the following:

a = 0.00023 P / 0.0033 (I plugged in the mass as well)

a = 0.0697 P (simply divided 0.00023 by 0.0033)

Ok. Now we have acceleration expressed as a function of pressure.
Now we have to answer how the pressure changes as the ball travels
down the barrel. I'm going to assume that the barrel we're using
has zero porting in it, just to make my life easier. :)

This brings us to Formula 3:

P1 * V1 = P0 * V0

This basically says that the energy held in a gas essentially
remains constant. Of course, this also assumes that the gas
temperature does not change. We'll make that assumption for
this exercise.

Our initial pressure (P0) is going to be 400 psi
(2.757 megapascals). The initial volume (V0) is 0.55 ci
(0.00000901 cubic meters). We can plug these two values into
Formula 3 and get the following:

P1 * V1 = 24.85 Newton-meters (i.e. Joules)

The volume of space behind the ball as it travels down the barrel
is going to be the volume of the dump chamber (0.55 ci) plus the
area of the barrel times the distance the ball has traveled.

V1 = V0 + A * x,

where x is the distance the ball has traveled, measured in meters.

We can then get the following expression for our pressure:

P1 = 24.85 / (V0 + A * x).

P = 24.85 / (0.00000901 + 0.00023 * x)

Ok. We now know how the pressure should change as a function of
ball position. We can plug this back into our acceleration
formula:

a = 0.0697 P

a = 0.0697 * 24.85 / (0.00000901 + 0.00023 * x)

a = 1.732 / (0.00000901 + 0.00023 * x)

or, if you want to keep all the variables as variables rather than
having the numbers plugged in...

a = P0 V0 A / (m * (V0 + A x) )

P0 measured in pascals (newtons per square meter)
V0 measured in cubic meters
m measured in kilograms
A measured in square meters
x measured in meters

Our acceleration should be in meters per second squared.

And there you have it... one acceleration formula. Keep in mind
that this does not take into account frictional forces experienced
by the ball as it slides against the barrel wall. These forces
are not always insignificant, though if you have a good paint to
barrel match and can blow a paintball out the barrel with ease,
you may well be able to ignore frictional effects.

I've got a semi-handy Microsoft Excel spreadsheet which calculates
a paintball's acceleration down a nonported barrel and determines
what the theoretical exit velocity should be. I'm working on
tuning this equation so that the ball exits the barrel at the
desired velocity and when the pressure in front and behind it are
equal. I can vary the pressure, initial volume, barrel length,
and frictional forces so far.

BJJB

[athomas]

Excellent. That's what we're talking about.

If it isn't too much trouble, could I have a copy of the excel worksheet. It would save me doing the same work all over.

thanks

[bjjb99]

athomas wrote:
>
> If it isn't too much trouble, could I
> have a copy of the excel worksheet. It
> would save me doing the same work all
> over.

I'll have to make sure it's reasonably presentable... after all, I created it to be "me friendly" rather than "user friendly". When I get it ready I'll post an attachment in .zip format, since it doesn't look like this forum supports .xls or .wbk. It's going to be an ancient version of excel (4.0), but the recent versions should still be able to read it.

BJJB

[bjjb99]

Well, I've made the spreadsheet as friendly as I could, and have zipped it up so I can attach it. Man, it's just under the filesize limit. I hope this works...

There are a couple of things to keep in mind when playing around with this spreadsheet. First, it does not necessarily represent reality, as it is only a theoretical treatment of the problem at hand. Second, it handles things a bit differently than what has been discussed... basing everything on very small increments of time (calculus a-la excel) rather than ball position.

I have yet to figure out why, but the spreadsheet fails to give even remotely close velocity numbers for an automag's dump chamber design (500+ fps from a 10 inch barrel at 400 psi input?!). I think this has much to do with my inaccurate guesses for the volumes of the power tube and bolt, both of which will cause an immediate pressure drop from the dump chamber initial pressure at the moment of gas release. Perhaps more accurate numbers for these two volumes would correct the spreadsheet results. There are also the matters of non-instantaneous gas relase from the dump chamber and gas leakage around the bolt and power tube (likely small?) to contend with.

Have fun playing around with it. Maybe you can improve some things here and there, though you may want to fiddle around with a copy in case things get out of hand. ;)

BJJB

[CHK6]

Let me first say I have really enjoyed this thread, I have learned a lot. I am 99.999% almost done in figuring out pressure drop in a pipe with compressible gasses. The following is a massive culmination of research I have gathered from the last three weeks and was able to cross reference verify with other sources.

Here is the generic formula that needs to be solved.

delta(P) = F (L/D) * [(p * u^2)/(2 * g)]

delta(P) is the absolute pressure drop, not guaged.
F is friction factor of material.
L is the length of the pipe.
D is the pipe diameter
p is avg. density at flow conditions.
u is mean velocity
g is gravity

To find (u):
u = Q/A
A = cross section of a circle.
Q = volume flow in entrance conditions. (ICFM)

To find (Q):
Q = (Z * R * T) / (60 * M * Ps)
Z is the compressibility of the gas.
R is universal gas constant
T is pressure temperature
M is molecular weight of the gas
Ps is pressure (PSIA)

To find (p):
p = (P1 / 14.7) * d
d is the density of air at amospheric temperature.

To find (F):
You need a materials chart

To find out if the flow of the gas behind the ball is turbulent calculate the Reynold's Number:
Re = (p * u * D) / y
y is absolute viscosity of air at atmosphereic pressure.
If the result of Re is greater than 4000 the flow of the gas behind the ball is considered turbulent.

Now all I have left is to plug in the numbers. Which I'll do this weekend when I have some time.

[CHK6]

This doesn't sound right. After some calculations I figured that with a 10 inch SS pipe with a mean velocity of 140 fps using Nitrogen with 80 degree weather the pressure drop is 2.142318 PSIG.

Now that's with a constant flow of gas for the length of the pipe. So if we started with ~28 PSIG we would end up with a pressure guage reading of ~26 PSIG at the end of the pipe. Giving use slightly less than 280 fps. This gives us the solution of show much max volume you need at the lowest pressure possible. Volume being the volume of gas the 10 inch barrel consumes.

So the flip side is how little volume can we get away with at the highest pressure?

Since we can't provide a constant flow of gas for the entire length of the barrel, (well we can, but why stop there and be in-efficient; aka gas piggy), we need to figure out what fixed amount of volume of Nitrogen is needed at under what preesure will accelerate the ball.

[steveg]

Looking at pbjosh's table and concluding that 200in3*lb
is a close enough for our purposes number, and that the
typical maximum output pressure for a fixed air tank is
850psi

200in3*lb/850psi=.235 in3 not suprisingly about half
the volume of the mag at 400psi.

Given the anecdotal nature of pb's table, it is remarkably
constant from marker to marker

so what makes a shocker so wasteful and an impulse so
efficient ?

[athomas]

If a valve output causes the level of thrust to be decreased by some means such as restricted flow or turbulence then the efficiency is reduced. The matrix does a better job than the shocker of maintaining initial higher pressure behind the ball and and then allowing the pressure to drop at just the right time to reduce the waste air flow out the barrel.

The chamber size vs pressure is critical. The barrel length is also a larger factor in lower pressure guns because the pressure is maintained for a longer period in order to allow slower acceleration to the desired fps setting.

A short barrel would be extremely inefficient on a low pressure gun. It takes a certain amout of torque to accelerate a ball to the desired speed. If the pressure is lower the rate of acceleration is lower. Therefore it takes the ball longer to reach the desired speed. In a short barrel, the distance is not there to allow that to happen. Therefore the pressure must be increased to allow a greater acceleration. The greater pressure combined with the larger chamber of lower pressure guns = larger amount of air used. Most isn't utilized and just pours out the barrel after the ball has left.

There is so much to consider. One thing that hasn't been discussed much is the effect of friction in most of the equations. Here is where the lower pressure guns gain back some of there inefficiencies. Typically, the effect of friction is a function of the square of the velocity. Since lower pressure guns accelerate the ball at a slower rate, the force of the friction is not as great in the early stages of the barrel as it is in higher pressure guns that achieve greater velocity earlier in the barrel.

Hope this helps.

[AGD]

You guys are doing so well with this I am going to jump in and share some data that I never let out in public. Here is the pressure profile of the Angel that you can use to determine accelleration rates. Virtually all paintgun profiles look like this except for the Matrix and Mag which take longer to get up to pressure. The Y scale is pressure and the X scale is time in tenths of milliseconds so 10 counts = 1 ms.

As you can see the pressure and therefore the accel. is not linear. The barrel was a dye 14" with a sensor at the end. To make matters worse the vent holes in the barrel let out the pressure before it gets to the end.

AGD

[bjjb99]

Tom Kaye wrote:
> You guys are doing so well with this I am going to jump in and share
> some data that I never let out in public. Here is the pressure
> profile of the Angel that you can use to determine accelleration
> rates. Virtually all paintgun profiles look like this except for
> the Matrix and Mag which take longer to get up to pressure. The Y
> scale is pressure and the X scale is time in tenths of milliseconds
> so 10 counts = 1 ms.
>
> As you can see the pressure and therefore the accel. is not linear.
> The barrel was a dye 14" with a sensor at the end. To make matters
> worse the vent holes in the barrel let out the pressure before it
> gets to the end.

That's a fascinating plot! I think it's wonderful that you're willing to share data like this. I've taken this plot and extracted the pressure/time coordinates as best I could (Adobe Photoshop plus some elbow grease), entered them into an Excel spreadsheet, and calculated acceleration, velocity, and ball position as a function of time.

However, I've run into a bit of a snag.

In order to accurately determine acceleration, we need to know the mass of the nylon balls that were being shot. When I used an average paintball mass (about 3.3 grams), I ended up with a final velocity of around 213 fps and a total distance traveled of 9 inches from the ball's starting location before we get to the "ball exits the barrel" marker on the plot. This indicates to me that the mass of the nylon ball used is less than 3.3 grams. Based on the plot provided, I'd estimate the nylon ball mass to be around 2.3 grams, which seems low to me. Perhaps the resolution of the plot is just not enough to perform an accurate acceleration/velocity/distance calculation.

Out of curiosity, how do you measure pressure as the ball is travelling down the barrel? I'm guessing you've got a port drilled into the barrel right near the breech, with a pressure transducer mounted there; outputs from the transducer go to either a digital oscilloscope or a digital acquisition board in a computer. I would like to know what kind of transducer you're using, since the only ones I've seen available (Omega.com) require pretty large ports (>>0.125 inch diameter) to mount them. I don't want to put a 1/4 NPT hole into the side of a barrel and then try to fire paint. ;)

BJJB

[AGD]

BJ,

I don't like to give away the details of the sensors we use but we do drill a hole right at the barrel breach interface to feed the sensor.

The nylon balls are about 3 grams but where you are probably running into problems is in the pressure numbers. The sensor is dynamic so it's the delta of the curve shown. It actually starts about 5-10 psi negative so you have to add that back into your numbers. So that makes the peak pressure about 95-100 psi. Run those numbers and it should bring up your velocity.

We do use a super high speed DAC board.

AGD

[bjjb99]

Tom Kaye wrote:
> The nylon balls are about 3 grams but where you are probably running
> into problems is in the pressure numbers. The sensor is dynamic so
> it's the delta of the curve shown. It actually starts about 5-10
> psi negative so you have to add that back into your numbers. So that
> makes the peak pressure about 95-100 psi. Run those numbers and it
> should bring up your velocity.

When I first looked at the plot, the curve looked like it started below zero pressure. I figured it required baselining, so I went ahead and did so prior to calculating any accelerations. The peak pressure I obtained at that time was 94.6 psi, give or take a few hundredths.

Using the plot, I came up with a scale factor of 0.4484 psi per pixel for the vertical axis, and 0.02188 milliseconds per pixel for the time axis. These are based on the 0 to 100 psi scale taking up 223 pixels, and the 4300 to 4400 time scale (10 ms) taking up 457 pixels. I used the lowest point to the left of the pressure spike to represent zero pressure (baselining), and scaled everything accordingly. My results for a 3 gram ball end up with the ball reaching the "exit point" marked on the plot after 10 inches of travel and a final velocity of 233 fps.

What I think has happened here is the plot just lacks sufficient resolution to take numbers from it and get an accurate result. Even if I can't get 300 fps out of my calculations resulting from that plot, it's still a very interesting look into the dynamic world behind a paintball as it flies down the barrel.

You mentioned that the pressure sensor is "dynamic so it's the delta of the curve shown." Does this mean that the sensor is measuring delta-P as a function of time, and the curve shown is basically the integration of that delta-P from time zero to time T? If this is the case, what caused you to use a delta-P sensor rather than an absolute-P sensor? Do delta-P sensors have a faster response time? I imagine that you probably need on the order of microsecond resolution for accurate data capture, and I have absolutely no idea what the response times of pressure sensors are (yet). :)

BJJB

[AGD]

Yes the dynamic sensors we use have faster response times. We actually use both depending on the situation and the time resolution required. It's also possible our scale is off because we have to pulse 100 psi air into the sensor to calibrate it. It is by no means an exact method. I would just scale the curve to get the right speed.

AGD

[Redkey]

Pressure transducers, at least mine anyhow, have a typical full scale response time of about 0.1 ms or about 1/10,000 of a second.

I'm not sure about the whole dynamic pressure transducer conversation. There are two main types of pressure transducers... absolute and differential. My understanding is that a differential pressure transducer measures the difference between two pressures, ie they have two inputs. An absolute pressure transducer is basically the same only it has one input... with the second pressure being open to air.

DACs run at many speeds, My card, for example, will collect about one channel at 1 MHz, 1,000,000 samples per second. Splitting that into multiple channels will reduce the sampling rate ie three channels will each run at about 333 KHz depending on how your card is configured.

bjjb99 if you're going to build your own system I can help you out in private since it sounds like the AGD folks don't want the details discussed in public. It's not exactly a cheap project and it's definately not simple unless you live in the world of testing.

How can you tell exactly when the ball starts moving by looking at the plot?


Later
Jack

oh... and...
68 cui @ 3,000 psi =
68 in*in*in X 3,000 lbs/in*in = 204,000 in-lbs
once the units are cancelled.

[AGD]

Redkey,

Yes we do use an AD card but I don't know what the max rate. It's multi channel so I think it depends on how many you scan.

The peak of the graph determines when the ball starts moving because it expands the chamber volume. We used to put a sensor in the breach but they correlated so well we just look for the peak now.

AGD

[bjjb99]

Redkey wrote:
>
> bjjb99 if you're going to build your
> own system I can help you out in
> private since it sounds like the AGD
> folks don't want the details discussed
> in public.

I think I've got a pretty good idea of what needs to be done. For the time being, this is just a set of thoughts rolling around in my head; I currently lack the funds and the workspace to set up a decent testbed.

> It's not exactly a cheap project and
> it's definately not simple unless you
> live in the world of testing.

Well, at least I've got something going for me. I have been responsible for experimental design, specification, setup, execution, and post-collect data processing for more than a couple of years during my various work-related incarnations... nothing dealing with high speed pressure measurement, though. I agree that this won't be one of these "rubber band and chewing gum" budget experiments. The combination of fast response time, small packaging, high precision, and low cost is extremely rare when it comes to instrumentation/sensors.

Time to add this project to my ever-growing list of things to do once I get a workshop set up. :)

BJJB

[Redkey]

AGD...

from the plot it looks like the arrow is a bit below the peak of the curve... I was wondering if there was another measurement taking place.

Does your system also measure volume of air used? Or do you somehow calculate the volume based on the duration of the event?

thanks
Jack

[AGD]

We are not concerned with volume right now. The arrows just generally point to the peaks there are no other measurements going on.

AGD

[hitmanng]

I have been following this post with interest and thought it was time to jump it.
Remember that there are a lot of factors determining the amount of pressure needed. Most importantly how much air is wasted and not converted into kinetic energy and the friction on the ball.
Remeber Tom's graph measures the pressure behind the ball. As the gas expands it moves the ball forward decreasing the preasure behind the ball. When the ball (cork) exits the barrel (or porting is hit) the presure drops to zero.
CHK6 did the math showing that an average pressure of 28 psi is needed over a 10 inch distance. AGD has verified that with wastage in escaped air and friction, 35 psi is closer to the real number.
I have now seen 3 numbers for the amount of travel time the ball has in the barrel. In CHK6's example 0.003 sec. In the graph of the Angel above 0.004 seconds and in the Mag from barrel tip #1. 0.006 seconds. This actually makes sense. An increase in initial presure will cause an increase in the accelleration of the ball. You would of course have to stop the excelleration earlier than 10 inches if you don't want to go over 300ft/sec.
In the Angel example above the pressure goes from 100 psi to 0 psi over 10 inches. The Angel runs out of pressure before it runs out of barrel. This is the most efficient process.
You could easily use a lot more presure and have the barrel run out before the pressure. This would be very inefficient of course. Theoretically as long as all of the force if the air pressure is used before it exits the barrel all guns should have the same efficieny ie it takes the same amount of force to move the same object the same distance.
The only factors that we have control over are the volume and the initial pressure of the gas. But guns do not all have the exact same efficiency. Why not?? The bolt.
Where does the bolt come it? The bolt has mass. Is moved by air and drastically changes the volume of the chamber.
Everything I have seen so far indicates that you are shooting a blowgun not a paintball gun.
Any thoughts??
Hitmanng
Killer of sacred cows

[MikeCouves]

Whooooooooooosh!! There it goes, all that stuff right over my head :D. How old are you guys that do this? Is this like university grade math? Sounds pretty tough.

[AGD]

Having the barrel run out before the pressure has the interesting effect of giving you tighter velocity groups which means better accuracy. Wasting gas in this case can be a benefit especially to a back player who needs the range and can go in tighter to 300 fps. The worst thing to do is have too much barrel and the ball starts pulling a vacume before it leaves. This actually does happen on a poplular low pressure gun I won't name. With too low a chamber pressure the air runs out faster than you would like.

AGD

[steveg]

Tom just out of curiosity. Most low pressure markers have
a reputation for very good consistancy , so is the fact
of running out of pressure before barrel of real practical
concern, or academic interest

RedKey thanks for the in-lbs thing, I thought it might be
that but the bit if math I had ran away as fast as it could
and hid as soon as I finished school. Use it or lose it:confused:

[Redkey]

I would guess... without the plots to prove it...

it takes a certain number of ft-lbs of air to launch a ball.

Higher pressure guns use a smaller volume of high pressure air to fire the ball ie... short duration high pressure spike.

Low pressure guns use a larger volume of low pressure air to fire the ball ie... long duration low pressure spike

In theory, a gun running at low pressure should use the same amount of uncompressed* air as a gun running at high pressure to fire a ball at 300 fps. Although, I keep on seeing posts saying how inefficient low pressure guns are, I have never seen data to prove it.

*by uncompressed I mean the volume of air released into the atmosphere when the gun is fired.

So, I don't think all low pressure guns have the problem Tom is talking about... just the ones that don't use enough low pressure air.

This brings up another question... what affect does the barrel porting have on this phenomena?

Tom, have you actually measured negative pressures after the ball has passed a certian point in the barrel?

Interesting...

[CHK6]

Actually I didn't do so well in math in college. Mainly stems from to many red-eye nights playing ROTT over the net and never using the correct symbols that intructors wanted to see on papers and tests. Blahh, what do they know? The answer was correct.

I have been looking at other marker designs in how they deliver gas and possibly the flow behavior that comes from that design. There are equations that help explain how gas flows when the gas passes junctions. I found the angle of the junction makes a difference in how the gas flows and the pressure released. Porting in nothing more than miniture junctions in a large pipe.

I understand that porting is usually done at a 90 degree angle straight down to the center of the pipe. But can anyone explain why angled porting hasn't been done? Could it be that foward angles create small graders like a cheese grader and backward angled porting would only help with excess pressure?

I think these are interesting questions. Not in the sense of major break throughs, but just tweaking the small teaks and possibly creating unique barrel designs specific to a certain marker.

I'm also curious as to why o-ring seals in barrels haven't come about? I know that it's cooler to have a two-piece barrel or a sleeved barrel design, but a simple o-ring inside the barrel can do the same things and you won't need a ball dente.

That's my ten cents, inflated to thirteen cents, and Uncle Sam taxes it to 2 cents.

[steveg]

I suppose the reason that porting holes are perpendicular
to the barrel is simply because it costs less.
I'm guessing that most barrel manufactures drill
the holes and whatever other decoration on the same lathe
that that the barrel itself was turned on. As an alternative
the barrel, after turning would be mounted
on a rotary table (4th axis) on a machinig center. All
things considered, the first method would be the prefered
method because the part is handled only once if at all.
Angle heads for lathes are available but are very expensive
and very easy to break.
So the short answer Cost.

[AGD]

Guys,

Yes we have actually measured negative pressures in the barrel that go away once the ball exits. If this is an important factor or not we can't say without looking into it further.

AGD

[steveg]

Here is a link for the math for energy stored in compressed
air. www.media.mit.edu/people/aries/portable-power/node5.html#SECTION00030000000000000000
appropriately, the example uses a 68/3000 paintball tank

Math guys, get to work!

[BEEFYSAUSAGE]

so to get a barrel with good efficencey and that shoots a tight group the gas pressure in the barrel should be as close to 0 as posible before before the porting or end of barrel(non ported).ok if that could be done would the variable size of paint be to much of a vairable to make it feasible(vairing friction)or would it not have that much affect on the speed of the pellet?
BEEFY.

[Ityl]

Now, with the gas being wasted by the ball exiting the barrel before the end of the barrel, couldn't this mean that the point of where the ball changes from acceleration to deceleration occurs later on. So wouldn't this create slightly more range?

[AGD]

Ityl,

This has been a long standing myth in paintball that a ball decellerates differently out of different guns. The fact remains that when the ball exits the barrel it hits a 170 mph headwind that starts decellerating it instantly. There is no chance for it to do something different.

AGD

[athomas]

The negative pressure thing had me stumped for a moment or two. I was trying to reason why there would be negative pressure behind the ball when the entire volume of air initially stored in the chamber would still be in the barrel and chamber. I think I have an understanding. Correct me if I am wrong.

The ball is accelerated to a velocity in the barrel determined by the initial pressure, the chamber size and the valve opening/flow rate. At a point in the barrel where it reaches its peak velocity, it also has its maximum kinetic energy. At some point farther down the barrel, the kinetic energy stored in the ball will allow it to maintain some/most of its velocity which is greater than the expansion rate of the compressed gas following behind it. This will create a vacuum effect and give the negative pressure reading.

The moment of zero pressure reading not maximum velocity would be the desired exit point from the barrel, even though there would still be wasted gas following behind the ball. This would give best shot grouping/less turbulence. The maximum velocity point on the other hand would give best air efficiency.

[bjjb99]

athomas,

I think you've got the basic explanation down, though the ball is not exceeding the expansion rate of the gas behind it. Instead, the pressure behind the ball has simply dropped below the normal atmospheric pressure. The ball is now feeling more pressure ahead of it than it is behind.

If you think of it not as "negative pressure" but rather "pressure lower than the ambient atmosphere," it becomes easier to visualize. The paintball is initially accelerated by a much greater pressure behind it than in front of it. As it travels down the barrel, the volume behind the ball increases, and the behind-ball pressure decreases accordingly.

If the barrel is long enough, at some point the pressure behind the ball will drop below the ambient pressure present ahead of the ball, and the ball will begin to decelerate. This is the point where the behind-ball pressure "goes negative" relative to the ambient atmospheric pressure. If we include frictional forces from rubbing against the barrel walls, then the point at which the paintball begins to decelerate will not be coincident with the pressure "going negative".

Keep your fingers crossed, 'cause I'm gonna try to attach a picture showing the forces/pressures involved.

Many pressure sensors output what is known as gage pressure (psig), which is pressure relative to ambient conditions. A gage pressure sensor behind the ball will measure negative pressures when the absolute behind-ball pressure drops below ambient.

BJJB

[athomas]

In order to have a negative pressure (compared to ambient atmosphere), we must have a vacuum effect. Eg. If the inside of a five inch long barrel is suddenly lengthened to 10 inches (ball moving down a barrel) without allowing the addition of more air to allow equalization of atmospheric conditions, then the 14.7 psi (0 reading on the gauge) would be 7.35psi (-7.35psi on the gauge).

The pressure inside the barrel of a paintball gun firing a paintball never theoretically reaches 0 psi (relative to atmospheric pressure). As long as the ball is in the barrel it is holding the chamber pressure from exiting the front of the barrel. The only way to create negative pressure in the barrel is to create a larger volume faster than the available air can fill it up. This is where the paintball guns with the lower chamber pressures have problems. The available air in the chamber is forced through holes(nozzle) in the front of the bolt. The rate of discharge is related to the pressure in the holding chamber. As the gun is fired and the ball accelerates down the barrel this low pressure gets even lower. Eventually the kinetic energy of the accelerated ball allows it to maintain a speed causing the barrel volume to increase faster than the rate of air discharge from the chamber. Here is where we have the pressure differential we are talking about. The pressure sensors read a negative pressure (vacuum). Higher pressure guns like the mag don't experience this phenomenon to the same extent if at all because the rate of air discharge from the chamber is greater due to the higher chamber pressure.

[Ityl]

So you're saying that it's impossible for a ball to still accelerate after it leaves the barrel? Or that it's just that the amount is trivial?

It must accelerate some when it's out of the barrel, and the faster the ball is moving the longer it would accelerate out of the barrel. I'm not sure of the numbers on this, they may not even be measureable easily.

[athomas]

In order for a ball to accelerate, there must be a force behind it greater than the force in front of it. The moment the ball leaves the barrel, the forces behind it disappear. Any residual gases dissipate in all directions of least resistance. The frictional forces of air plus the pressure in front of the ball cause it to immediately start to decelerate.

In conclusion there is no acceleration beyond the barrel.

Any gun that causes acceleration beyond the barrel would have to waste a hughe amount of air to keep the ball engulfed in the pressure blast.

[bjjb99]

athomas,

The pressurized gas behind the paintball is capable of expanding at far greater velocity than that of the paintball itself, even when it is only slightly above ambient pressure. Reference Tom K.'s statement regarding transonic flows in the thread titled "FEM model of a paintgun?". The restriction in flow caused by the bolt/valve tube/etc. should not be enough to limit this expansion to the point where it falls below the paintball velocity.

The pressure inside the barrel of a paintball gun can reach zero relative to atmospheric pressure (0 psig), Tom Kaye mentions this in his February 13 post to this thread; a "popular low pressure gun" which he won't name actually ends up with a behind-ball pressure below atmospheric pressure prior to the ball exiting the barrel.

BJJB

[athomas]

BJJB:

Looking back at our previous posts, I think we are saying the same thing.

The real question is why does this happen sooner in some guns than others. The test using the unnamed gun was conducted using a vented barrel. This could/probably did contribute to the pressure reaching relative 0 within the short time the ball was in the barrel. Further movement of the ball down the barrel due to built up kinetic energy would definately create the vacuum effect which would result in negative pressure.

In a mag with a nonvented barrel, the the negative pressure phenominon would theoretically occur somewhere around 35" down the barrel, unless the ball can travel down the barrel faster than the air can follow it.

Lets try an experiment. Use a nonvented barrel. Tape up one end leaving an opening the size of the automag valve(use a straw). Insert a squeegy from the open end of the barrel. Place it all the way at the closed end of the barrel. Now tighten the squeegy so that it forms a seal. Pull it from the barrel at some high velocity. If there is no vacuum created in the barrel then the rate of expansion/compression of air through the valve can keep up to the ball traveling down the barrel. If there is a vacuum created, then a full speed ball can create a vacuum partly because the air in the barrel and chamber cannot keep up at low pressures. Note-this only occurs when the pressures are low, usually at the end of the expansion cycle.

[Ityl]

there would some force on the paintball after it leaves the barrel, but not a lot, so the more I think about it, the more I shoot down my idea, along with you guys said. Kind of like the idea of electricity travels the path of least resistance, but not totally, some always goes down the more resistant path.

And why would creating a vaccuum be a bad thing? couldn't you use it to your advantage by creating a vaccuum, then opening the bolt and let a rush of air down the barrel to aid efficiency? And it would pull the next ball into the chamber.

I want a gun dyno, I'd never be bored...lol.

[ShooterJM]

Originally posted by Ityl


I want a gun dyno, I'd never be bored...lol.

Boy I know that feeling.....and a wind tunnel!

[Mr. Grumble]

I need to visit Blue more often, this is great reading.

Seems to me that negative pressure would be difficult to achieve, with regularity, in a Mag. The open bolt blow forward would allow atmosphere to flood in through the breech in an attempt keep you at 0 psi. To reach negatives with any regularity you would need to fire from a closed bolt marker.

Now, if you had a long, un-ported barrel on a closed bolt marker you could generate a good sub-atmospheric pressure during firing. And if you cycled the bolt before the paintball were to exit the barrel (exposing the breech to the atmosphere), you would generate a sudden rush of atmosphere in through the breech. If a second paintball were waiting to drop into the breach, it would be exposed to disparate pressures. Therefore, atmospheric pressure would accelerate the paintball into the breach in addition to the acceleration of gravity.

Heaven help us, we have entered the Shadow Lands called 'ball suck'. :eek:

Mr. Grumble

[As a side note, what is the sound signature of a marker that fires at a negative psi like?]

[athomas]

As long as the ball is in the barrel of most paintball guns with a standard barrel length, there is pressure throughout the length of the barrel. If the bolt opens while that pressure is present it will flow up the feed tube. This is known as blowback.

Once the ball exits the barrel, the sudden gush of excess air out the barrel end creates a vaccuum effect which is the negative pressure which can be measured.

On most guns you can see this effect by dry firing them. Without the ball holding back the air, all the air gushes out the front of the barrel creating this vaccuum effect. Put a piece of tissue in the feed tube and dry fire the gun. It will suck the tissue into the barrel.

Autocockers are known for this effect because they are a closed bolt design and the bolt timing is such that it doesn't open until the ball has exited the barrel. If the timing is such that the bolt opens immediately after the ball exits the barrel, you will experience this vaccuum. Its kind of interesting.

There are exceptions to this rule because of different markers operating at different pressures and chamber volumes as well as barrel lengths and porting. These all affect the air movement and pressure within the barrel.

[Paladin]

Hi guys,
I just had to put my two cents in here.

I was pretty good at math when I was a kid but it seems I've forgotten most of what I learned in basic hi school algebra 35+ years ago.:)
Back in the day when we only had 12 gram cartridges to work with, it was far more important that the gun be as efficient as possible than it is today with everyone using bulk tanks with either compressed air or CO2. I'm still a big fan of CO2 for paintguns because I could never find a real good reason to endure the costs, bulk and weight of the typical HPA system on mu gun.
All these numbers and calculations are great I guess but I never learned to use them effectively. However, I have learned some things from many years of testing and development work in the process of making paintguns as effective as possible. What I have learned from experience is that it takes X amount of energy to get a ball up to speed and there is only X amount of energy available in the supply tank, regardless of size or the type of gas in it.
The trick to an efficient paintgun is to deliver that energy to the ball under conditions that allow for a short burst of air that can run as freely as possible to push a ball to speed in the shortest distance possible and metered so that propulsion load ends at about the same time that the ball gets to desired speed; and that should happen just before the ball gets to the muzzle. Efficiency is determined by the metering process AND what happens after the air is dumped. Slight interuptions in the air flow between the valve and the back of the ball can make a big difference in how effectively the burst of air can impart it's energy to the ball. ie: A little trick that can easily pick up a few fps on an Amag is to streamline the back edges inside of the face of the face of the bolt with a Dremel tool. It will only add a couple fps to the chrono averages but every little bit helps. Generally speaking, as a paintgun gets more efficient, it also gets more accurate. This because an efficient shot generate less muzzle blast that could kick the ball off course.
In most cases, lower pressures do not necessarily mean better efficiency because we are dealing with a relatively fixed velocity limit. Lower pressures require slower operating speeds, extremely well tuned air passages between the valve and ball,longer barrels and generally cause more wasted gas/energy in the process of getting the ball up to speed.
I never know what the actual pressure stored in the valve chamber of a gun is until after I finsh getting it tuned for optimum performance. For most paintguns, somewhere around 400 to 450 psi HPA (a little less with CO2) seems to present the best acceleration characteristics and maximum efficiency for painballs at field speeds.
I'm sure some of you technical types will dissagree but I just wanted to point out that there is a great deal more to firing a paintgun "efficiently" than what you can figure out with a scientific calculator. What I've learned comes from about 18 years of a great deal of trial and error development work toward getting a paintball to go where and when I want it; And that started after about 25 years of working with firearms and balistics with the same goals in mind.

[AGD]

Welcome Glen! I told you that you would like this place!!

:)

AGD

[Vegeta]

Welcome to AO Mr. Palmer!

You'll love Deep Blue... I have been misproven many times by the people that post here. And it is very suprising to see all the math and physics being applied to paintball here... this is hands-on stuff.

I have been off this subject for a bit so I am going to read upwards a bit and then post my comments if I ahve any...

[Vegeta]

OK I read up a few posts and saw that some of you were talking about vacuums created by the ball travelling down the barrel. I first found this a few weeks after getting my first semi-auto, the good ole M98. Some people were talking about the blow-back and how if the air isn't vented properly, balls will get blow up the feed neck and will cuase feed problems at higher ROF's. I didn't get this totally, becuase the bolt was moving forward... and.. well.. I just had to see this for myself. I took a square of toilet paper and my 98 outside. gassed her up. I split the 2 plys in half and laid one sheet on top of the elbow, And fired the gun. I found that it sucked the paper into the tube a bit. Interesting.

If we could harness this power a bit more effeciently, maybe someday we could haev mroe effiecient feeding. Tippmann has already came out with their new air-powered ram agitaded hopper, based off the old F/A hopper design. We saw it a few months ago on Warpig as a prototype, and now it is going into production on the new Tippmann A-5, which is shipping in a few days (County Paintball took pre-orders).

But that is a bit off topic, and valves are my thing.. not feeding.

[cphilip]

Welcome Mr. palmer. We are very honored to have you here.

[Paladin]

First off, I want to thank you all for welcoming me here. As I said before, much of the discussion here is way over my head in terms of the "science" involved so I still have to operate on practical experience and a K.I.S.S. principle understanding of the launching of a paintball.
Question: If shooting a paintball can generate a vaccuum in the barrel, what does that tell us about what is actually going on ? What it tells me is that the gun is not tuned very well because peak velocity happened long before the ball got near the muzzle. Then when the propelling gas runs out of push, the ball has to carry the rest of the way down the barrel on energy alone, sucking wind behind it and loosing/wasting energy. If the ball starts decelerating while it is still in the barrel it can't keep up with,or carry as far as a ball that doesn't start decelerating until it leaves the barrel.

[FooTemps]

Wow Mr. Palmer... that made a lot of sense to me. I guess practicality always underlines brilliance. Good methods to work with in my opinion, how long did it take you to tune your paintball guns to have good efficiency and power?

By the way, WELCOME!

[Vegeta]

Wow, that did make alot of sense. If there was pressure from the gas behind the ball the entire way, then the ball wouldn't be sucking air. But it seems like the gun's valve gave a burst, then let off, leaving little force on the ball after it reaches a certain point in the barrel (porting might have a role in this.....). So... What we want is a steady stream of air behind the ball all the way down the barrel. We want it to be enough air to propell the ball fast enough (290 fps) but we also want to keep it rather low pressure for gas efficiency sakes. What if we had a valve that let out a slow, low pressure stream or air at first.. to get the ball going down hte barrl.. and then lets out a larger voulume shot of air after that, the keep built pressure and volume behind the ball. Its not just pressure on the ball that we want, beacue the ball is going down the barrel, the volume of the gas decreased, and the ball is having to pull the air behind it, cuasing that vacuum. So if we get a phhhhhhh of air followed directly by a pop of air, we will keep enough gas behind the ball, hopefully without being a gas hog. Not the first 'phhhh' of air wouldn't need to be very high presure, just enough to get the ball moving. But it would have to be held out a bit longer, so it maintains a presistant pressre/volume behind the ball. Then comes the higher pressure, but shorter burst of air, followed directly after the low low pressre stream. Keep in mind the ball is still in the barrel. The higher pressre, short burst of air will push all the air in the barrel with the ball out the barrel at 290 fps. Whew.

Did you guys understand that? It would take a very, very comeplex valve to test that theory out, and after all, it is just a theory. I don't think such a thing would be produceable via a mag valve... a complex poppet valve maybe.
I'll think on that one. First, you guys see if that makes sense to you.

[Paladin]

Tom,
You were quite right. I do like it here. Very interesting group, to say the least. :p

Some ??? to AGD,
Given a standard production AutoMag on compressed air, "average" humidity and barometric pressure, decent paint, etc. How far from the face of the bolt will the ball travel to reach 300 fps ? and how far... to reach say 270 fps ? Now, same scenario but with CO2?

FooTemps,
It took me several months after I got my first two paintguns to get a handle on making my equipment as effective as possible. On my 3rd time out to the local "Survival Game" field I bought one each of the two guns that were available at the time in order to see which I could get the most out of for my game. (a Nelspot 007 and a Sheridan PG; PG = forerunner of the PGP; no pump handle)Anyway, with my gunsmithing background it was real easy to figure out just how they worked but figuring out how to make them work better was a different matter. My game skills developed rapidly but my equipment was keeping me from excelling. Too old to out-run 'em, so I had to out-gun 'em to get to the flag.
Accuracy of course was an issue and the first thing I did to both guns was polish the barrel; however, efficiency was of greater concern. Paintballs then cost $2.50 for a 10 round tube ($.25 each). A 12 gram cartridge was a buck and you could get about 10-12 shots out of a cartridge. I hated wasting money but it was more important to gain a tactical advantage in the game by lowering the frequency of maximum vulnerability when you run out of gas and had to change cartridges; which at that time was about a 30 second process. (An issue that I resolved a short time later)The idea being to run 'em out of gas and rush 'em while they change cartridges.
I knew how to optimize the internal ballistics in firearms but this was going to take a whole new line of thinking. The first step was numerous trips to the library to gain an understanding of CO2. Then, basic air flow and fluid dynamics concepts were explored. Leading me to the conclusion that I had to meter the release from the valve effectively and then let my paintgun "breath" freely. Armed with a new load of relevant information, a little common sense, a garage full of tools and a huge determination to have better equipment, I went to tinkering and testing the results of every little thing I did. I also had a chronograph to work with. A chrono wasn't part of the game yet but it proved invaluable in determining if any changes I made had positive results. Certainly better/cheaper than counting shots per cartridge. Quite simply, if I made a change and the velocity went up, I was headed in the right direction. If the velocity didn't change I could move onto another detail but if it went down I had to back up and figure out why; undo it and then move on. I was able to double the efficiency of my paintguns pretty easily and eventually got to nearly triple the "good" shots from a cartridge over stock configurations but that was a long winded process. Well worth the effort though as it created some major advantages on the field. It turned out that I was able to get better overall effectiveness out of the Sheridan valving format than I could get with the Nelson system so I stuck with the Sheridan. Along the way, we got pump handles, gravity/direct feed and I came up with a quick change unit for the 12 grams (QuikSilver)which gave me the firepower of "constant air" a bit before bulk tanks were even introduced. But that is another story.:) Palmer's Pursuit Shop came to exist largely because many people asked: "What would you charge me to do my gun like that?"
Sorry for rambling:
Take care all.
Later
Glenn

[Vegeta]

Yep.. paint cost $2.50 for a 10 round tube and we had to walk 25 miles uphill in the snow to get em!


People complain about prices of paint nowdays... of course demand went up greatly when semi-auto markers came out... but thats another topic.

[FatMan]

Hey all.

Not to disagree with Glenn (who is one of my heros - I used to own Typhoon BB9) but slight suction at the feed tube does not neccesarily mean there is vacuum in the barrel. The air blasting down the barrel AFTER the ball is expelled will cause some draw at the feed tube - unless the chamber remains closed well after the shot (like in a closed bolt system). In fact, air blasting *past* the feed tube can cause suction, the same way the wind blowing past a chimney causes a draw that pulls the smoke out.

If your paintgun is running out of air well before the ball leaves the barrel, something is wrong!

All that said, Glenn is certainly right on with what he's saying. All of the equations are just rought approximations of what's really going on. There are just too many inter-dependent variables to do a decent analytical job with this. More is to be gained through working with the system as a whole - and I think Tom and Glenn are two of the most experienced at this - which is why they make the best paintguns in the world.

FatMan