# Paintball Spin Physics - Getting to the final Answer

Show 40 post(s) from this thread on one page
Page 1 of 9 12345 ... Last
• 11-18-2002, 03:17 AM
AGD
Paintball Spin Physics - Getting to the final Answer
Gentelmen,

I have posted a framework of info in the data thread. This is from an extensive study we did in the early 90's. The data is representative of our findings.

Currently on the table:

Spin is the only major factor accounting for paintball inaccuracy. Promoted by Pbjosh

Closed bolt operation has an effect on overall accuracy. Promoted by Glen Palmer.

The paintball flight is subject to "knuckleball effect".

Spin may or may not be possible because of the liquid in the paintball.

Barrels have something to do with accuracy.

Seams have something to do with accuracy.

Balls distort with the impact of the air blast.
Balls distort when leaving the barrel.

Ok lets have a pointed discussion on the subject. For those of you just reading this, this thread is a continuation of the "closed bolt" thread found here.

AGD
• 11-18-2002, 05:06 AM
nippinout
Tom, could you elaborate on the ball exploding pictures?

Thanks.

Moving on...

So if we do have spin, to have any effect on accuracy it must be on an axis differing from it's path.

Whether or not the seams affect flight is what we're after. However, Glenn found differing velocity due to seams. Seams have different effects before and after barrel?

Good discussion!
• 11-18-2002, 09:02 AM
Ostwar
Is it possible to make a paintball with:

1) No seams or 2) completely filled with paint (no air pocket) or 3) completely round (or as round as possible)

Does the impact of the bolt distort a paintball and therefore accuracy?

Considering the high speed movement of the bolt forcing the paintball into the breach of the barrel at up to 20 times per second (closed or open bolt). Even if the bolt is light (delrin or similar) the momentum would have an effect on impact energy being transferred to the edge of the paintball (also this would be far less than the gas pressure released on the ball during firing).

Would a paintball rotate while it is being loaded by the bolt, thereby changing the position of the axis of the seams and affect accuracy as a result?

My thoughts for the brain pool,

Shaun

P.S. Is AGD really Tom Kaye? I would find it hard to believe he has the time to be on these forums, but if he is, kudos to him for connecting with the players at a more personal level.
• 11-18-2002, 09:43 AM
ezrunner
Really
AGD really is Tom Kaye, and he is one of the few people in the
industry who bothers to back up any of his claims with data.

Tom: I come from a precision shooting background and would
like to add a combinatorial statement to the list. This
comes from the realm of bolt action rifle tuning where we
fit the bolts to the breeches
and the barrels to the stocks.
(ie bedding and free floating)

The mechanical repeatability of the positioning of the components
in and around the breech such that the ball is in the same
relative position on each firing contributes greatly to accuracy.

i.e. The barrel should be tight enough that when the ball seam is turned
such that it is at a 90 degree angle to the bore, so that the
seam is only touching the bore at two points, that there is
minimal gap between the ball and the barrel.

Now that we have a good paint to barrel match, we make sure
the bolt stops in the same position before the shot is
fired. This means that the air is always released at about
the same angle of incident to the projectile so that the forces
acting on each ball are nearly the same.

This will ensure that any spin is rather consistent and that the
paint is consistent down the barrel.

What this buys us is mechanical repeatability. A
closed bolt has a small delay even under rapid fire where the
bolt can come to rest. The higher the rate of fire the
smaller this difference is in comparison to the better electros.

A well fitted bolt to the breech ensures that the bolt
stays in the same place for
each shot.

I think this set of conditions
leads to accuracy in any mechanical
system and projectile systems in general.

I know that GP (aka palladin) had referenced something akin
to this in his post on barrels and chambers.

I would love to hear Tom and GP chime in on this?

How does this align with the designs both of you espouse?

The mag had the chamber built into the barrel and the blazer
and typhoon series had closed bolt operation.

How does each guarantee these circumstances, or are they
considered?

-rob
Clemson #12
• 11-18-2002, 11:39 AM
pbjosh
Thank You AGD,

For starting this thread and dropping the photos.

I think we have to define 'Spin' first. I realize there might have been some confusion.

'Spin' as I have been using it is the perpendicular rotation of the ball to its flight.

Not the horizantal rotation like an object shot from a rifled barrel. In fact, since that is so hard to produce in a paintball I think it wouldn't have even been thought that way.

To find the issues with accuracy we need to look for something that is an affect of firing a ball that still affects the ball after it has fired. There are other things that affect the ball, and we do need to explore all of those also.

I think that a Closed Bolt operation helps in keeping spin to a minimuim. The ball starts from a position in the barrel, and is only affected by the travel through the barrel and the air applied to it. In an open bolt system the ball is physicly pushed forward, travels in the breech, then across a barrels rim, into the barrel, and while still in motion, the ball has air applied to it. In the Open system there is alot of added affects to the action of a ball.

A paintball would only be affected by a "Knuckleball effect" only if it wasn't spinning. If it has some small spin that would cancel out the non-rotating action of a knuckleball.

As for "Spin may or may not be possible because of the liquid in the paintball" I personally think that the Flatline barrel is a good example of spin being possible. Since the spin is still affecting the ball until it has run out of forward momentum, I would hazard a guess that the creamy liquid center of a paintball doesn't affect it too much. It can lower the spin faster than if the ball didn't have a liquid center, but I would think that would add more accuracy, to a point, after a bit.

Barrels have alot to do with accuracy, but again I think the incurred spin from one barrel to the next is an issue. The paint to barrel match is important for several reasons, but I think an barrel that is in-accurate would be one that puts more spin on the ball. A short barrel would put less spin on the ball for the most part. The ball can't spin as much if it has less barrel to rub against.

Seams have something to do with accuracy. They do, but I would think mostly in the preshot arena that causes the ball to spin before it leaves the barrel.

"Balls distort with the impact of the air blast.
Balls distort when leaving the barrel. "

Again, in the preshot arena the distortion, if any (personally I think the distortion would only be about .001"-.002" or so, if it happened) would only have an outside accuracty affect if the ball incurred spin from the distortion. The ball would return to normal after it left the barrel I would think.

Okay-

Tear it all apart!

Josh
• 11-18-2002, 11:41 AM
314159
Re: Paintball Spin Physics - Getting to the final Answer
Quote:

Originally posted by AGD
Closed bolt operation has an effect on overall accuracy. Promoted by Glen Palmer.AGD
i think that this would be better phraised as the firing system has an impact on the overall accuracy of a paintball. because the same firing system in open or closed bolt configurations will have the same accuracy.
• 11-18-2002, 11:52 AM
ezrunner
RE PBjosh
Paint to Barrel relations

For a given setup on a marker there will be an optimum
barrel of either design.

For a one piece barrel, the longer the barrel, the more
consistent it will be, and the more surface before venting
can aid in air efficiency. This is offset by the drag down the
barrel when the air is nolonger accelerating the ball. At that
point, the barrel should end or should step out to a second piece.

In a two piece barrel, the section that touches the ball
should be long enough to give adequate use of the air expended,
while not causing drag on the ball. I don't know of a 2 piece
that I think causes drag. A one piece 14" barrel seems to
shoot really well, but the 12" tubes are just as good for my
purposes.

The venting in a 2 piece does matter. We have observed with
freak barrel systems that changing from a 12" to a 14" tip
on an AKA Cocker running at about 180 psi (goes to valve
open time for those who understand cocker tuning)
can jump the velocity 20fps or more. The unvented area of the freak tip apparently allows
for some acceleration to still occur even though the paint is not
being sealed all the way around.

Has anyone here used the bolt from Cooper-T for the autococker?

It puts backspin on the ball like a flatline barrel does.
It works best with a small amount of oversize in the barrel
so that the fit is not as tight, and once you break a ball,
you have a mess.

I am not sold on backspin yet but I will be doing a good deal
of testing on this bolt once our cocker bodies come back from
the CNC shop and we build them out. One marked advantage is
that as you turn the marker, the ball begins to hook around.
On a speedball field this could be a devastating advantage
as you take away your opponent's cover. I'm not sold
yet, but we will be doing testing.

-rob
Clemson #12
• 11-18-2002, 12:09 PM
314159
Re: RE PBjosh
Quote:

Originally posted by ezrunner
For a one piece barrel, the longer the barrel, the more
consistent it will be, and the more surface before venting
can aid in air efficiency. This is offset by the drag down the barrel when the air is nolonger accelerating the ball. At that point, the barrel should end or should step out to a second piece.

i have once heard someone say, that shorter barrels are more accurate, because of their short lenght, any imperfections on a paintball will not have as significant of an impact, like they would in a longer barrel. i have not thought this through, and am putting this out on the table.

i think that the main deal in "paint to barrel match" helping out accuracy is getting a barrel small enough, so the ball dosen't wobble, and big enough, so that it does not exploide a paintball. i think that the main benifit here, is not allowing a paintball to wobble in a barrel. i think that you could have a straight riffeled barrel, with about 4 rifilings, that would be about 1/8 in wide each. these would be tight on the paintball (maby .678), and the outer area, could be like .700 in dia. the rifilings would hold the paintball tight, not allowing it to wobble, and the area of the barrel that is not riffled, would alow the paintball some room to expand, when it is squeesed into the rifilings. i think that this would keep the paintball from poping, and keep good "paint to barrel match" accuracy over a wider range of paint sizes (at the cost of a little efficency)
• 11-18-2002, 12:25 PM
pbjosh
I would have typed a bit more total, but my 2yo decided it was a good time to come in and erase everything I had typed already!

Josh
• 11-18-2002, 01:23 PM
ShooterJM
Quote:

Originally posted by pbjosh
Thank You AGD,

For starting this thread and dropping the photos.

As for "Spin may or may not be possible because of the liquid in the paintball" I personally think that the Flatline barrel is a good example of spin being possible. Since the spin is still affecting the ball until it has run out of forward momentum, I would hazard a guess that the creamy liquid center of a paintball doesn't affect it too much.

Josh

I agree entirly. Both the Tippy Flatline and the Z-Body demonstrate induced spin by the trajectories of the paintballs.

AGD - Thanks for posting the detailed photographs and test results! This will make for great reading!

ShooterJM
• 11-18-2002, 06:39 PM
hitech
Am I missing something?
I don't see enough data presented to draw any conclusions. Certainly not where spin is concerned. I did not see any indication in any of the tests presented that the paintball was "spinning". While it is very interesting, it doesn't appear to be enough, in my opinion, to draw any conclusions from. Did I miss something?

Edit: Thanks Tom. THAT makes much more sense now. I didn't want to assume that the marks on the ball were anything more than shadows.
• 11-18-2002, 07:31 PM
AGD
Ok this is what you do with the data.

1. look at the marks on the ball and determine how far it rotates between each flash exposure. Use that,the distance between shots and the known FPS to determine what RPM's the ball is rotating at. When your done with this you should be able to answer the following questions:

1. What is the balls RPM?
2. Is there only one spin axis or does it corkscrew on two spin axies?
3. Does the spin maintain, speed up or slow, down range?
4. When the ball spins it has higher surface speed on one side and lower on the other. Using the RPM tell me the difference in surface speed, this figures into the Magnus effect.

Once you do this homework then we will go on to correlating the spin to the X,Y ball position in flight.

Don't post until you have this info, the data is in front of you not on PBN.

AGD
• 11-19-2002, 05:30 AM
Havoc_online
ok, I feel lost because I don't see any pictures to look at. However some thoughts just came to mind.

Quote from Glenn(quoting someone else)-
Quote:

The ball remains round and is infact forced round by gas pressure.

Not entirely true as it does not take into account the distortion of the ball as it is compressed from front to rear by the g-forces of acceleration.
Would it not be reasonable to assume that the distortion of the ball would be greater on a closed bolt marker since it is accelerated instantly, as opposed to an open bolt marker that gives two levels of acceleration(THREE on a level 10 Mag) thus giving the ball more time to accelerate. Actually on a level 10 mag, considering the foamie it may be 4 levels of acceleration. Lacrosse balls fly fast, but consider how they accelerate compared to a baseball. This raises the question if an open bolt marker deforms a paintball any less than a closed bolt marker. Maybe acceleration over a longer period is the key to the accuracy debate between open and closed bolt markers. Even golf balls deform under the same high G-forces. If deformation of the paintball does occur it would flatten the front which would cause spin once it left the barrel. If acceleration over time would deform the paintball any less, it would make the ball spin less giving less counterforce for the fill(see below). However the accuracy debate is too close to believe that any deformation between either type of marker would make a paintball spin above 6000rpm even making a difference.

Quote:

Spin is the only major factor accounting for paintball inaccuracy. Promoted by Pbjosh

Spin may or may not be possible because of the liquid in the paintball.

Seams have something to do with accuracy.
These statements are all related to what I believe. Since the ball is under so much forward momentum the fill is compressed to the back of the shell giving the ball a somewhat stable flight axis before it leaves the barrel. The seam would not cause enough drag to counter the force of the fill enough to make the paintball spin past the point of 6000rpm. Spin does not make a difference below 6000rpm due to the lack of counterforce on the fill. Spin beyond 6000rpm in the barrel only takes place if there is a unwanted variable such as oil/paint, bad paint/barrel match or intentional force is applied(flatline/zbody)before the fill is completely stable. Spin beyond 6000rpm achieved outside the barrel would be obtained by a ball that is badly deformed or highwind/rain/etc.

Therefore it is my opinion that with the current limitations of the weight of paintballs and the restrictions of velocities, as long as your paint fits your barrel the most consistent marker will be the more accurate marker. Although in the hands of a player, two things matter. Recoil under higher ROF which is a case of a level 10 bolt being lighter thus having less reciprocating mass. Trigger pull would be the other factor. Mags and cockers both have tuff triggers so electro's come into play. It's a good thing AGD makes a stock electro;).

If this makes sense great, if not, forgive me, I'm sick and sleepy:(
• 11-19-2002, 08:16 AM
bjjb99
Pics are in the Official Data Thread
Don't feel lost in your search for the pictures Tom is referring to; they're in Deep Blue's Official Data Thread. It took me a while to find them. Now I feel kinda silly because I didn't go to the Official Data Thread right away, especially since I now see that Tom mentioned that the data was located there in his original post to this thread. I guess I just missed that sentence the first time through.

Yep, I'm awake... honest... really, I zzzzzzzzz. ;)

BJJB
• 11-19-2002, 10:15 AM
pbjosh
Havoc_online:

There is one flaw in your logic.

The spin I am refering to is axial spin perpendicular to the direction the ball is traveling. The spin you are refering to is spin on the same axis as the ball is traveling.

These have severly different affects when going 200mph through an atmoshpere. Do not confuse the two.

When talking about Magnus affect, which is caused by perpendicular spin, the affects are in-stability and hence, in-accuracy, unlike the affects you are talking about.

We are NOT talking about horizantal spin. Which is what rifleing on a barrel does to a bullet.

Josh
• 11-19-2002, 11:32 AM
pbjosh
I just found this.

http://www.marist.edu/physics/applets/magnusg.html

After playing around with some figures from the Data Pics AGD dropped I will trying running it through.

EDIT:

The parameters don't come close to what we were looking for, sorry.

Josh
• 11-19-2002, 01:21 PM
Ostwar
Pbjosh: Since you are not reffering to rifling spin direction, then is what you are saying refer more to the flatline barrel concept? Do you desire to minimize spin altogether on a paintball, giving it a flat or non-spin affect?

Shaun

BTW: your link to the Magnus force applet, excellent! (although I wish to go below .1 on the Mangus force scale, maybe I did it wrong).
• 11-19-2002, 01:51 PM
hitech
Quote:

Originally posted by AGD
...look at the marks on the ball and determine how far it rotates between each flash exposure...
I assume that you are guaranteeing that the paintball does not rotate more than 360 degrees between exposures. Correct?
• 11-19-2002, 02:11 PM
pbjosh
Shaun,

The Magnus effect only really affects the ball when it is spinning perpendicular, not horizontal. A non-spinning ball will do the 'knuckleball' like in baseball. A slight spin is best. But for the most part we can't control this spin. A gun that incurrs alot of spin will shoot the ball all over the place IMHO.

Also, after looking into it a bit, what we are trying to do is minimize the spin, or the Magnus Effect related to the spin of a ball. So having a dimpled surface would only help in the Flatline or related systems. If it had a rough or dimpled surface the ball would swerve MORE. In other sports the balls surface is rough to optimize spin and rotation, or the Magnus Effect, so you can do all the curveballs and fun stuff you want to do to it.

As for the pics, to study this better we would really need video footage so we could count the number of rotations over a period of time. Right now we do have great high speed footage, and due to the closeness of the shots we can see the ball tumble quite often. Like hitech mentioned, this is not a perfect way to trace the rotation of the ball though. The pics are great, but not under-minding what Tom did, for this theory to be analyzed best we would need to trace a realtime pattern of the ball, plus induce spin that we can control (like the Z-body) which is a bit out of our reach right now. A camera that could take pics like that is way out of our price range-

Josh
• 11-19-2002, 03:28 PM
bjjb99
Some noodlings before I get home. :)
Why would we need a high speed camera? A good 35mm camera with a bulb setting, a dark environment, and an accurately timed high speed strobe light should be more than sufficient. The faster the strobe, the more data we have to play with, of course. I think we can safely discount any more than a 180 degree rotation per strobe flash in the AGD tests; see below for details.

Assuming the measurements in test 101 are accurate, the ball travels approximately 6 inches between successive stobe flashes as it leaves the marker at approximately 280 fps. This means the stobe flashes are about 1.8 milliseconds apart. I don't know if it's possible to determine what the "further down range" strobe rate is since we don't know the ball's velocity at that point, so I'm going to look only at the near-barrel portion of the test.

Eyeballing the images (I'm not at home right now and thus lack access to proper image processing software), I'd say the ball in test 101 spins around 15 degrees +/- N*180 degrees per strobe flash, where N is an integer. This accounts for the discrete nature of the strobe and the fact that the ball could additionally make one or more complete 180 degree spins and we might not notice it. The spin axis in test 101 appears to be nearly vertical, judging from the underside view portion of the image. There may be a slight precession of the spin axis, but I cannot identify this well from the posted images; I might do better once I get home.

Let's assume the ball spins 15 degrees per strobe flash to start with. This means that the surface velocity of the ball is around 0.089 inches per strobe flash, or 4.1 feet per second; this yields a differential surface speed of 8.2 fps for opposite sides of the ball. The "against the wind" side of the ball sees a 284.1 fps headwind, while the "with the wind" side of the ball sees a 275.9 fps headwind. I'm not all that familiar with the Magnus effect, so I'll leave it to others to utilize this data (if it's is can be used at all) in determining the lateral forces induced as a result of spin.

Now, let's assume the ball spins 195 degrees per strobe flash (15 + a 180 degree rotation that we cannot discern due to the discrete nature of the strobe). Then we end up with a surface velocity of around 53.5 fps, and a differential velocity of twice that. The "against the wind" side of the ball sees 333.5 fps and the "with the wind" side sees 226.5 fps.

Suppose the ball spins -165 degrees per strobe flash (15 - a 180 degree rotation that we cannot discern). Then we end up with a surface velocity of around 45.1 fps and (again) a differential surface speed of twice that. The "against the wind" and "with the wind" sides of the ball have swapped locations, since the spin vector is pointing in the opposite direction this time.

Personally, I don't think the ball spins more than 195 degrees between strobe flashes... 195 degrees per 1.8 milliseconds is already 301 revolutions per second, or around 18000 rpm. Centripetal acceleration is given by V^2/r, if I remember correctly. The surface velocity at 195 degrees per strobe flash is 53.5 fps (16.3 m/s) and the radius is 8.6 mm... this yields a centripetal acceleration of 31000 m/s^2, or around 3150 g's.

In contrast, during firing the paintball experiences a minimum linear acceleration of around 12000 m/s^2 (1220 g's) to go from rest to 280 fps in a 12 inch barrel. A linear acceleration of 31000 m/s^2 yields an exit velocity of around 450 fps. I have no idea whether paintballs can survive being fired at such velocities, but I suspect they don't more often than do. This leads me to believe that centripetal forces resulting from 18000 rpm spin would result in paintball self-disassembly upon exiting the barrel.

I think we can safely limit ourselves to the +/- 180 degree spin regime, and may well be able to ignore the +/- 180 degree portion altogether. This leaves us with at most three scenarios to plug into the Magnus effect for each spin measurement performed.

Happy Magnus-ing! ;)

BJJB
• 11-19-2002, 05:37 PM
Pstan
Gentlemen,

I dont quite know whether my thoughts on this subject will matter to most here........Certainly Mr. Kaye can move this post or delete it as he sees fit, but I would like to join the general discussion having read this post in it's entirety. I come from a background beginning in firearms that has spanned around 20 years now and have been involved with paintball for around 4 years. I am a tinkerer by nature, as my Grandfather and Father were trained as Watchmakers and Jewelers. I hold a MA in History and Education, but have taken courses in every conceivable field, so all of the mathematical jargon here is not totally foreign language to me. However, dont ask me to calculate anything........if I need that done I'll go a to a friend of mine who was a Professor of Mathematics at Georgia Tech University and is now retired.

What I see here are basically 2 lines of thought. One believes that mathematics can describe the relationship of accuracy in 2 different types of paintball guns that cycle differently conclusively. In other words......numbers dont lie. The other group seems to fall into a category that doesnt quite refute that claim, but has misgivings that calculations on paper disprove what they have seen through experience, observation, and personal knowledge. And, in order not to leave anyone out, there are positions here that represent views from both. However, I think the first 2 groups make up the majority.

There are a few points to consider within both groups. First, Mathematics does not prove, or disprove everything that exhists. Einstein proved mathematically that the universe is finite. Other scholars have proved mathematically that the universe is ever-growing and constantly expanding. Who is correct in that argument? Are the numbers lying in one case and not the other? Second, as I look above me everyday I notice that the Sun is moving around the Earth. At night I notice that the Moon is always following my car everywhere I drive. Are my observations of heavenly motion correct simply because I literally see it that way? Or is that really what is going on? Point being, what is seen isnt always what is true.

Whether all of you realize it or not, most seem to be camped out with your respective group and unwilling to do what seems to me to be the optimum thing. That optimim thing is to do another test and start the argument over in a debate where everybody has the same data. Whether one side wins or not ( ie Closed-Bolt v Open-Bolt ) is a moot point to me, but it would be interesting to see the findings in a joint effort.

What do I propose?
1. 2 markers should be constructed. Basically billet aluminum in a stacked tube config.
2. 1 open bolt........1 closed bolt.
3. 1 barrel to be used on both.
4. Both should drilled and tapped for a mounting braket to be used in the test firing.
5. Both should be tested with the same power source and regulating system at the same pressure.
6. Only ammo that is "perfect" should be used......I seem to remember talk of a paint that constitutes this variable being created at AGD? ie not real paint, but of perfect roundness and constant weight.
7. And lastly, all the dimensions of the 2 markers should be the same.......inside and out. Ball position at moment of firing, length, and so on..... of course the closed will need pnuematics mounted and the open will need a valve that provides the gas to recock. Other than those variances, the guns will be the same.

Might this not lead to a better conclusion?

Hopefully, I've not offended anyone. Certainly that has not been my intent. Is this an area that is an acceptable course for this debate to go?

Respectfully,

Pstan
• 11-19-2002, 07:12 PM
Top Secret
That test could be done by an autococker timed to shoot open bolt, then reconfigured and timed to shoot closed bolt. If I get bored enough to swap my cockers 3-way hoses, I'll recreate WARPIG's test using my gun.
• 11-19-2002, 08:14 PM
pbjosh
The thought on the video camera-

That would remove all doubt that there could have been an other sort of tumbling in the ball, and would give an accurate position of the ball at all angles.

Thoughts on guns to use-

We would want a gun that is currently produced. I know of a person who has a open or closed bolt angel ran by the racegun grip. It would be PREFECT for this test.

Can anybody give us some other thougths as to issues that can be incurred in the gun, and affect the ball after it has left the barrel, besides Magnus affect? I want to hear it

Josh
• 11-19-2002, 10:09 PM
AGD
BJ,

You can eliminate the possibility of the ball rotating more than 180 deg in my pictures. We spaced the strobes at varying widths to determine the general range of spin RPM's on most balls. From that info we spaced them as you see them in the pics so we could measure the spin without missing a turn. Bravo BJ! You get my respect for actually looking at the images and trying to figure something out.

Josh,

So you are saying that the pics are not good enough data but we should continue to debate what we have experienced? You really think high speed video is required? How about we just go through the motions and see what we get?

AGD
• 11-19-2002, 10:39 PM
pbjosh
AGD-

Sorry for the confusion, but people can look at the pics and say- "hey, it might have turned 180+ degrees between shots" etc. (and they did)

Not in any way or form do I think the film is not good enough, it is quite a treat. When I get time I will do a couple of figures myself.

And I agree, lets run as much out of the pics as we can. High Speed video will be a total pain in the........

As for debating what we have experienced, I think we should be looking for other issues besides spin or velocity that can affect the ball, that someway can be incurred in the gun but affect the ball in flight. Part of getting on this so hard is I REALLY want a better explanation than the old "all guns shoot the same velocity, so they all shoot the same distance" BS that has been floating around like Flat Earth Gospel. There is something else, I think it is spin. It might actually be ZAP elves. But unless we throw it out to the wolves and beat it around, add some science, then we won't know, and the stupid arguement and hype will still float around till somebody makes the 'New Science'and hypes the dickens outta it.

This is the perfect place to get it right. Lets do it.

I will freely take the Devil's Advocate for this one. I DO think it is Magnus Effect. Lets just get our brains in on this and really figure it out.

Josh
• 11-19-2002, 10:40 PM
Redkey
hmmmm....
This is interesting.

When were these tests run?

Were the paintballs checked for balance before testing? My thought here is that the heavy spot would tend to rotate downwards... This effect would probably be minor compared to other spin effects this close to the muzzle. But, you never know...

Was the barrel cleaned after each shot? Were any balls shot with paint in the barrel to see if spin was induced that way?

I assume there is alot more data... were the findings consistant from shot to shot? or was there a ton of variability?

Is there really air in paintballs? I thought they were filled in a pressurized system... where the paint forced the flexible gel into the two halves of the mold.

Does anyone here use image analysis software?
• 11-19-2002, 10:46 PM
flanders
paintball seems are a good thing, in some ways

fallowing the 2 pionts on barrel to kepe the ball on target is a good thing the ball is stabalized while letting the right amount of air past not to cause blow back

as for airpoctes they allow a ball to not be so birrtal it pops in teh gun, while not makeing a shell even harder, if a bakl infact has no spin forward or back then the airpocet won't matter if it's facing backwards, or if it's roatating at a constant rate so tat it's never forward back up down etc then it will be ok do to compensation

barrel do ahve something to do with accurac, not lengthj ( i dun know if theres a barrel to big or 2 small) but quality, if they are rifled to much and the ball has spin goes pop, if the barrel has burs pop, if the barrel is to big, bouncy bouncy pop bad accuracy, if the barrel aint supper clean pop, if the barrel has odd porting can cause poor release of air causing spin, to tight air can't get through in the right way or ball gets stuck or shell peels off

the ball can distort with high pressure bursts but it would have a reverse translation (as in all liquid filled objects) impact on oen side creats lump on other side this may or may not be a good thing (depending on spin) if spin occurs left or right ball witll be good havign a bullet effect, if ball spins up or down bad ball is lopided pops or screws it up more

as for spin not hapening with liquid, if there was no air pocets then the ball would be hard like a solid object or atleast it doesn't impact or adjust every thign is filled, ball still spins, if there is an air pocket, and the liquid can still move then yes will cause lopsided pickle ball spin. but if the buble does not move it creats a weighted zone creating a similer odd spin, if spin occurs

General hypothesis

If spin lateral spin (left to right)occurs then one or many of the factros will effect accuracy

If spin longitudanal spin (up and down)occurs then one or many of the factros will effect accuracy
• 11-20-2002, 03:41 AM
AGD
Redkey,

There is a LOT more data, so much that I am not about to put it up. We did this extensive study in the early 90's. The data presented is representative of our findings and if properly analized should point to some pretty strong conclustions.

In fact I already have all the answers to all these questions. I am going through the motions with all of you to see if the general public can, or is willing to, understand the reality of paintball accuracy.

Flanders,

Where are you from?

AGD
• 11-20-2002, 09:02 AM
ShooterJM
Quick question.

In the tiff files named p1010027 and p1010028 (The two pictures of the scatter chart looking targets titled "View looking down flight path of ball"), could you tell us the distance at which the readings were taken and if the paintballs were prescreened for roundness? I'd also be curious to know if there is any weight difference between the nylon test balls uses and an average paintball.

Thank you.

*EDIT*: I count 8 seperate issues from the first post. Is the intent for all to be addressed in this thread?
• 11-20-2002, 09:07 AM
Pstan
Essentially, what I've seen in the last few posts from Mr. Kaye relates what I was saying in my original post above. There is so much bias in this discussion that it renders moving forward an unlikely event.

The original question was whether a closed-bolt marker was more accurate than an open-bolt marker. Why I ask is the debate raging over other variables? From my perspective, it is simply the bias everyone is bringing with them. The original question has not been answered.

I proposed a new set of tests with 2 new shooting platforms that removed as many variables as I could think of in the short time I wrote the article. If others can think of more we need to remove feel free to add them. The new shooting platforms remove the bias that one brand of gun is better. The same air system removes the bias that how the platforms are given power affects the test. And so on......until we come to the only variance in the 2 being the type of actuation.

Run the test at that point. Answer the question at hand. Then post the results. Data will be available at that point. After doing that, the variables can be added back to the test until verifiable proof of what actually effects accuracy can be attained.

Lastly, science does not become accepted science until it is published, poked, prodded, redone, refuted, and/or ultimately proven. The scholarly world works in private, and speaks in public.......until that is done on this issue debate will rage.

Respectfully,

Pstan
• 11-20-2002, 09:42 AM
bjjb99
Can we even measure the Magnus effect?
Woo hoo!

I found a webpage which describes the mathematical foundation for the Magnus effect. It is located at the following URL, and describes the effect for rotating cylinders of infinite length:

http://www.mathpages.com/home/kmath258/kmath258.htm

I think it could be applied to our paintball, at least as a first cut approximation. After staring blearily at the equations, we come up with

L = - (rho) * v0 * (gamma), where

rho is the density of the fluid,
v0 is the velocity of the fluid (relative to the object in question), and
gamma is something called the circulation, defined as the line integral of the flow velocity around a closed loop.

What gamma basically means for us is "take the surface speed of the object and multiply it by the object's circumference". Thus,

(gamma) = vc * 2 * (pi) * r, where

vc is the circumferential (surface) velocity of the object,
pi is 3.14159 or thereabouts, and
r is the object's radius.

Let's plug in some of the data derived from the test 101 picture.

rho = 1.293 kg/m^3 (reasonable value for the density of air)
v0 = 85.34 m/s (280 fps)
vc = 1.25 m/s (4.1 fps surface speed)
r = 0.0086 m (radius of a paintball 0.68 inches in diameter)

So from this we get

L = -1.293 * 85.34 * 1.25 * 2 * 3.14159 * 0.0086
L = -7.45 (units?)

I'm not sure what the units should be. Doing a bit of unit analysis on the equation for L, we have the following:

L-units = (kg/m^3) * (m/s) * (m/s) * (unitless) * (unitless) * (m)
L-units = kg/s^2 ???

That sure isn't a unit of force I'm familiar with. We're missing a distance unit in the numerator somewhere, and darn if I can find it. Any help, anyone? :)

I also have happened across the following webpage, which gives a different equation (of similar form) for the Magnus effect:

http://carini.physics.indiana.edu/E1...ing-balls.html

Here they describe the effect as follows:

M = cM * (rho) * D^3 * f * v, where

cM is the Magnus force coefficient (1.23 works pretty well, according to the webpage),
rho is the density of the fluid,
D is the diameter of the object,
f is the object's rotational frequency (rotations per second), and
v is the velocity of the fluid (relative to the object).

If the Magnus force coefficient is unitless, then a unit analysis of this equation actually ends up with units of force coming out of it. Let's plug in some numbers derived from test 101:

cM = 1.23 (unitless?)
rho = 1.293 kg/m^3 (reasonable value for the density of air)
D = 0.0173 m (0.68 inch diameter paintball)
f = 23.1 rotations/s (15 degrees per strobe flash, one strobe flash every 1.8 milliseconds)
v = 85.34 m/s (280 fps)

M = 1.23 * 1.293 * 0.0173^3 * 23.1 * 85.34
M = 0.016 N

So for that amount of spin we end up with a Magnus effect force of 0.016 newtons. For a 3 gram paintball, this force results in an acceleration of 5.3 m/s^2, or right around 0.54 g's. Let's assume this equation has given us a correct answer, and see what the picture can tell us based on what we've calculated.

I am going to define the "first" strobe as the first image of the ball after it has exited the barrel, and incrementally name each successive ball image to the right of the first strobe (second, third, etc.).

An acceleration of 5.3 m/s should deflect the ball approximately 8.6 microns between the first and second strobes. This deflection is nearly two orders of magnitude smaller than the spatial sampling in the image (around 0.6 millimeters per pixel for the "bottom view" portion of test image 101). So even if the Magnus effect is at work, we simply can't see it from strobe to strobe. So let's look at the first and last strobes in the (strobes 1 and 5).

In this situation, the time interval is four times as large. Assuming the acceleration resulting from the Magnus effect is constant throughout the measured time, we should expect a deflection 16 times greater than that predicted between strobes 1 and 2, or around 140 microns (0.14 millimeters). This deflection is still smaller than the spatial sampling in the image.

If the ball is spinning at 15 degrees per strobe flash (and based on my other spin calculations and Tom's additional comments, I think we can safely assume the ball is not spinning at 195 or -165 degrees per strobe flash), and if the formula I used above is reasonable and accurate, then the high resolution pictures we have of the test are simply not sufficient to detect the resultant Magnus effect.

I looked at the "bottom view" portion of the test 101 picture to see if I could see any horizontal deviation in the ball's path, and I noticed something interesting... the laser aligned string is not straight. It curves slightly in the image. This leads me to believe we either have a camer/lens perspective effect going on here, or the string is vibrating during firing. The blast of air that escapes the barrel could be moving the string around.

I attempted to correct the slightly curved string by using Photoshop's transformation tools, but had little success. It seems that the transformation I'm looking for just isn't available in my version of Photoshop. Instead of measuring each ball's position from a single reference line, I generated local references corresponding to the string's location at each ball's position. I measured the following offsets:

Strobe 1: -4 pixels (-2.48 mm)
Strobe 2: -2 pixels (-1.24 mm)
Strobe 3: -2 pixels (-1.24 mm)
Strobe 4: -1 pixel (-0.62 mm)
Strobe 5: 0 pixels (0 mm)

These offsets are greater than the Magnus effect alone would suggest, unless the Magnus equation I used was incorrect. They may be the result of the escaping gas buffetting the ball around during the first few milliseconds of flight.

Well, that's about all I've got for now. Time to go do some work that actually fills up a paycheck. :)

BJJB
• 11-20-2002, 10:56 AM
Redkey
Quote:

Originally posted by flanders

as for airpoctes they allow a ball to not be so birrtal it pops in teh gun, while not makeing a shell even harder, if a bakl infact has no spin forward or back then the airpocet won't matter if it's facing backwards, or if it's roatating at a constant rate so tat it's never forward back up down etc then it will be ok do to compensation

As I struggle to read this and make sense of all your spelling errors / typos my only thoughts are that if you ever wish to be taken seriously you should read your post before submitting it.

Could you please explain how an airpocket in the ball will make the shell more brittle?

Quote:

Originally posted by flanders

barrel do ahve something to do with accurac, not lengthj ( i dun know if theres a barrel to big or 2 small) but quality, if they are rifled to much and the ball has spin goes pop, if the barrel has burs pop, if the barrel is to big, bouncy bouncy pop bad accuracy, if the barrel aint supper clean pop, if the barrel has odd porting can cause poor release of air causing spin, to tight air can't get through in the right way or ball gets stuck or shell peels off

Here you are making some statements about barrels and accuracy. Were I to make claims like this I would also present some data to support my claims.

Quote:

Originally posted by flanders

the ball can distort with high pressure bursts but it would have a reverse translation (as in all liquid filled objects) impact on oen side creats lump on other side this may or may not be a good thing (depending on spin) if spin occurs left or right ball witll be good havign a bullet effect, if ball spins up or down bad ball is lopided pops or screws it up more

An impact on one side of the ball will not cause a lump on the opposite side. The balls diameter will swell before a lump is created... unless of course there is a thin spot in the shell... it will be the weakest area and will deform first from the hydrostatic pressure.

If the spin occurs left or right the ball will hook left or right.

Quote:

Originally posted by flanders

as for spin not hapening with liquid, if there was no air pocets then the ball would be hard like a solid object or atleast it doesn't impact or adjust every thign is filled, ball still spins, if there is an air pocket, and the liquid can still move then yes will cause lopsided pickle ball spin. but if the buble does not move it creats a weighted zone creating a similer odd spin, if spin occurs

huh?

Quote:

Originally posted by flanders

General hypothesis

If spin lateral spin (left to right)occurs then one or many of the factros will effect accuracy

If spin longitudanal spin (up and down)occurs then one or many of the factros will effect accuracy

You could also say if the ball was blue then one or many of the factors will effect the accuracy.

Anyhow... I don't mean to be a jerk but, please review your posts before submitting them. Make sure they contain useful information that is similar to that being posted by the other people.

Thanks...
• 11-20-2002, 11:05 AM
AGD
Pstan,

This is about getting the facts and involves more than just an open or closed bolt issue. In paintball this is as close as we get to publishing.

BJ,

Nice job, that's the kind of effort I was looking for. The result of your investigation points out that the magnus effect is SMALL. So if the expected deviation from the Magnus effect is 1% and in tracking the paintball we see a deviation of 10% then we can safely say that another force besides Magnus is acting on the ball. We don't have to actually see it to make sense of it.

Do not let the string fool you, it was streached tight between two posts and only looks curved because the mirror was not perfect.

Everyone concentrate on test number 114 because we have the additional data for the flight path on that one.

AGD
• 11-20-2002, 11:19 AM
Ostwar
If Magnus force is dependant on spin, then what is involved to cause a ball to randomly move when little to no spin is applied. I take this from volleyball a sport in which if you serve the ball with a "flat" or minimized spin the ball will (for lack of a better word) "wiffle" in the air which will directly affect its trajectory. Is this a possibility in paintball?

Shaun
• 11-20-2002, 12:05 PM
bjjb99
Quote:

Originally posted by AGD

The result of your investigation points out that the magnus effect is SMALL.

I am withholding that conclusion until I recieve some validation of the equation I used to calculate the force resulting from the Magnus effect. It could well be that the equation I used applies well to things like baseballs and basketballs, but not necessarily to small, paintball sized spheres.

Quote:

Originally posted by AGD

Do not let the string fool you, it was streached tight between two posts and only looks curved because the mirror was not perfect.

Ah, a slight sag in the mirror would definitely explain the string curvature I was seeing. Hadn't thought of that.

Quote:

Originally posted by AGD

Everyone concentrate on test number 114 because we have the additional data for the flight path on that one.

I'll take a look at that one this evening and see what I can come up with.

While you're reading this, Tom, I've got a question I've been meaning to ask you. In the video tour of AGD's facility, you show off a large mirror you were grinding to make a large aperture telescope. Has the mirror been finished, and if so, what kind of figure does it have? I ask because if it still has a spherical figure it would be awesome to use it in some large scale Schlieren photography of the airflow behind the paintball as it exits the barrel. Even if it's got a parabolic figure it could still be used with a correction lens for such imaging. :)

BJJB
• 11-20-2002, 02:58 PM
Crimson_Turkey
Sadly I cannot post the evidence, but the raw egg theory does not applie ot paintballs. Paintballs will spin while in flight regardless of the liquid fill. Once the shell is set in motion it will not stop spinning as it moves through the air. As I stood leaning out of my window with a camcorder i filmed and egg pushed off the 5th story of an apartment building. A slight spin was imparted upon the egg as it fell. Earlier I had drawn a red line around the egg and in slow motion I could clearly see the line rotate. I would post the video if I could but this camcorder will not let me.

Eggs spin in the air. I think this is due to the lack of friction on the egg. When you spin an egg on a table it is grinding againt the table, causing friction. In the air there is a much smaller amount of friction on the egg. In addition, I think that because the shell of a paintball accounts for more of the total mass and volume when compared to the fill than an eggs shell to it's "fill" the paintball would probably spin better.
• 11-20-2002, 06:00 PM
flanders
california why?

*turns around with blunt object in hand*
• 11-20-2002, 07:05 PM
hitech
Here is a site with formulas. It is about the physics of paintball and he explains his formulas. bjjb99, you could see if your magnus effect formulas match his theory. You will find that he claims that the magnus effect must be determined experimentally. He does give a "guess", I believe.

There is also an applet that attempts to predict the trajectory of a spinning paintball.

http://home.attbi.com/~dyrgcmn/pball/pballIntro.html
• 11-20-2002, 08:10 PM
bjjb99
I've read significant portions of the site you mentioned before and have found it interesting if somewhat challenging to wrap one's mind around. I've computed the Reynolds number for a 0.68 inch diameter ball moving at 280 fps through air, and it comes out around 1.03x10^5. Judging from the graphs on the site you mentioned, this results in a positive lift coefficient under all conditions, instead of the reverse Magnus effect the site describes. It ends up following near to the curve fitted to the triangular shaped datapoints. Thus, I don't necessarily agree with the anti-Magnus conclusions the author describes.

Using test 101 data, the value for V/U used on that site would be (1.25/85.34), or 0.015. This puts our data point darn close to the left edge of the graph shown, and thus the lift (read "Magnus") coefficient is very very small to the point that it is difficult to even estimate it from the plot. I'd estimate the coefficient at around 0.02.

The site states that the Magnus effect force is characterized in a similar fashion to that of the drag force, and thus I used the drag equation to determine the Magnus force with a Magnus coefficient of 0.02. It works out to be around 0.04 newtons if I did my math right, which is about 2.5 times larger than the value I calculated using the equation on the carini.physics.indiana.edu site. Given the difficulty in estimating the Magnus coefficient from the plot, I think the result is close enough to say that either treatment is "good enough" for a first cut look at this phenomenon. I think the two methods agree with each other sufficiently to convince me that my original calculations are a reasonable approximation of the amount of displacement to be expected in test 101 (i.e. unmeasureable given the spatial sampling of the pictures taken during testing).

I am curious what this conclusion means in terms of the Flatline barrel system... I mean, I've seen floaters that just go and go and go coming out of that barrel, and I've seen horrendous curve balls when a Flatline gun is held sideways. I suppose the spin induced on Flatline-launched paintballs is much much greater than the mere 23 revs per second that test 101 exhibited, pushing the V/U point to the right and increasing the Magnus coefficient significantly.

BJJB
• 11-21-2002, 12:04 PM
Re: Paintball Spin Physics - Getting to the final Answer
Well, I've stared at the pictures until I'm cross-eyed and there seems to be very little that I can reach any value conclusions on that would fit into the ongoing discussion.
I cannot see anything here that addresses either, the issue of closed bolt versus open bolt or what effect internal ballistics has on the flight of the ball. However, I did do a bunch of shooting through powdered barrels as Tom suggested and arrived at the same conclusions that I reached through reading the scuff marks on paintballs shot through an un-powdered barrel. Results do seem to indicate that the ball does in fact distort or compress lineally from the forces of acceleration; causing it to tighten against the bore of the barrel for a period of time when launched.
My tests were done with a Blazer (closed bolt) operating with 400 to 450 psi input to the gun and firing Pro-ball paint at velocities of between 305 fps and 220 fps.
Only balls that demonstrated a consistent, loose fit in the barrel were used and each was blown through the unpowdered barrel with breath alone to relativly ensure consistent fit in the barrels before moving to higher pressures for launch.
In addition, each ball was chambered manually to ensure consistent positioning of the ball in the chamber prior to launch. Positioning of the ball was only made relative to the face of the bolt and did not address the position of the seem in relation to the axis of the bore.
Two barrels used: One with a straight bore of .690 and the other with an eliptically honed barrel, also with .690 base bore size but the center section of the barrel tapers out to .694 at 6" from the chamber and back down to .690 at 10" from the chamber. I did not have any Desenex brand powder on hand but Gold Bond, medicated powder seems close in consistency to Desenex.
The results: Almost every shot fired wiped the powder from the complete perimeter of the bore during the acceleration in the first part of the bore and then showed only a two-point track in the front half of the barrel. The length of time that the ball made full perimeter contact with the bore decreased as velocity was lowered. Also noted that the transition from full perimeter contact to a two-point track was more abrupt in the eliptically shaped barrel.
To further verify my results, the target was a bed sheet setup to catch the paint so I could read the balls as well as the barrel bore. Looking at the balls showed that the powder that was wiped from the bore was built up on the ball well forward of the center line of the ball with a wide "scuff" mark of imbeded powder. Thus indicating a significantly wide contact of the surface of the ball with the surface of the barrel bore.
Also, I did not see anything to indicate that any "spin" was happening inside the bore but I was not looking real close in that regard. My focus was on "data" that would indicate whether or not the ball would upset under acceleration. All indications to me are that the ball does in fact change its shape to a somewhat cylindrical form when pressure is applied and acceleration begins and the amount of distortion is relative to the velocity achieved. Your results may vary with different types of valving that might generate different rates of acceleration or different blast impact characteristics.

Now, to address some of the issues "on the table":

"Spin is the only major factor accounting for paintball inaccuracy. Promoted by Pbjosh"

In essence, a true statement IMHO. In this regard, I can only go by what I've seen which indicates to me that the less spin seen on a ball in flight, the more likely it is to go where it is intended. Less spin = tighter shot groups.

"Closed bolt operation has an effect on overall accuracy. Promoted by Glen Palmer." (two N's for this Glenn please :p

Actually, my contention is that closed bolt firing gives me the best opportunity to tune my gun (the whole gun) to maximize the effectiveness of the shot. Without appropriate setup and tuning, closed bolt firing is not likely to be any more effective than any other mode of operation.

"The paintball flight is subject to "knuckleball effect"."

It certainly is and I'd bet that we have all seen it at one time or another.

"Spin may or may not be possible because of the liquid in the paintball."

Spin is certainly possible but in relation to the effect on the flight of a paintball, is this discussion based on the lateral spin as would be imparted by rifling a barrel or the random spin generated by numerous other factors ??

"Barrels have something to do with accuracy."

This is one of the few points that I can see as being addressed in the "data" posted. The data in both pictures of "shot patterns" indicates that different barrels will achieve different shot groups. In both "shotpattern" jpgs, the Smart Parts barrel shows a tighter shot group than either, the Crown Point or Rail ? barrel. However, the tightest grouping seems to be shown in the lower left of the "shotpatterns2" jpg and I cannot make out what that barrel is.

"Seams have something to do with accuracy."

I believe that the seems themselves have less to do with overall accuracy than the size/condition and position of the seem on the ball which can and does effect the consistency of the flight path.

"Balls distort with the impact of the air blast."

A certain amount of distortion seems to be a fact. However, either as a result of impact of the air blast or the "G" forces of acceleration?

"Balls distort when leaving the barrel."

Lets hope not. Hopefully, the forces that cause distortion are relieved before the ball leaves the barrel. Although, the "smoke" tests seem to indicate a very interesting shape to the ball after it leaves the barrel.

The "smoke" shots also seem to show that there is not a collum of air being forced out ahead of the ball but that there is a small cushion of air around the ball. This brings up a question or three about the barrel and valving used for the smoke shots. Automag valving? Length of barrel? Venting in the barrel ?

The biggest problem that I run into with all of this is that I don't/can't use scientific calculations to prove out what I see and can measure. When you guys start spouting all sorts of scientific jargon and presenting formulas that often seem to me to be lacking in variables and such, you put the conversation well out of reach for me. I learned the old style math where 2+2=4 so I am relagated to believing what I see. When the things that I do can demonstrate consistent velocity readings and a tight shot group, I'm pretty well convinced that I'm doing something right. Then when something is changed and the results change too, it is quite easy to see whether or not the change was an improvement or not. Common sense and K.I.S.S. principle engineering has served me quite well for a long time. Unfortunately those things are just not accepted here.

Quote:

Originally posted by AGD
Gentelmen,

Currently on the table:

Spin is the only major factor accounting for paintball inaccuracy. Promoted by Pbjosh

Closed bolt operation has an effect on overall accuracy. Promoted by Glen Palmer.

The paintball flight is subject to "knuckleball effect".

Spin may or may not be possible because of the liquid in the paintball.

Barrels have something to do with accuracy.

Seams have something to do with accuracy.

Balls distort with the impact of the air blast.
Balls distort when leaving the barrel.

Ok lets have a pointed discussion on the subject. For those of you just reading this, this thread is a continuation of the "closed bolt" thread found here.