Paintball Spin Physics - Getting to the final Answer

[Paladin]

Originally posted by AGD
Glenn,

If a barrel did it's job perfectly every time and 100% of the spread was due to external forces then it would be a waste of time to try and improve it.

Tom, I have to agree with that statement but it is based on some pretty large and asumtive "IFs". It seems to assume that the barrel is the only factor besides external forces that can have an effect on the placement of the ball. One could also state that if changing only the barrel on a particular piece, produced a measurably improved shot pattern, it was not a waste of time to try to improve on it. It would also be a safe assumption that the way the ball was presented to the external forces, had a significant influence on the effects of those same external forces. Maybe such a barrel was just better suited to the forces behind the ball or maybe just better suited to the balls themselves. In either case, the result was to present the ball to the external forces in such a manner as to allow better consistency of placement of an inconsistent projectile.

[i]
The problem, as I see it, is that people spend 300 dollars for a barrel not knowing if it will make a 1% or 50% difference. [/B]

I know exactly where you are coming from and I whole heartedly agree. New and/or different is not always better.
Even more of a problem is that those same people will often find a way to justify the expence whether it provided an improvement or not. Style points have become far to important to some. [/B][/QUOTE]

[i]
In general I have to ask you, how much of an increase in accuracy have we really seen in 15 years? Given the fact the barrel prices have increased by 10x and are now honed and sized to perfection, what are we getting for the money? [/B]

That is a tough question to answer with any sort of brevity. In the context of this thread, there has been very little improvment in the overall accuracy potential of a paintgun in relation to barrels. Although, I believe that the typical paintgun of today will show measurably better results than the typical 'gun of times long past. It is much harder these days to produce significant improvments to shot groups by changing the barrel because of the general improvements to barrel production as well as the evolution of valving. Essentially, the guns that I built 15 years ago are every bit as accurate (for any one shot) as what we are producing today but I get better shot groups these days due to the better consistency of the air supply being used.

[i]
While you may be willing to spend big dollars on a 1% improvement most will not or at least would like to know what they are getting.

AGD [/B]

To the contrary; I am neither willing to spend my money in that regard, nor am I willing to take my customers' dollars for something that may not be of any real benefit. I've never been a proponent of having a bag full of barrels for your paintgun. Especially since most of my equipment is produced with non-changable barrels. However, we do offer services to ensure that a 'gun and its barrel are tuned to compliment each other and provide the opportunity to put the ball where you need it. I still believe that the valving of the 'gun is at least equally important as the barrel when in the pursuit of optimum performance.

[Crimson_Turkey]

Originally posted by yeahthatsme
if somebody would send me a rifled and straight bore barrel and a way to secure a marker so that it wont move when fired i would be perfectly willing to test the grouping differences between rifled and straight bore. i would use an automag with a max-flo air tank. so if i can get the stuff i will do the test.....

You would need the barrel to be exactly the same except for the rifling though. Unless you can get armson to make you a non-rifled stealth barrel this might be hard for you. You may also be able to get a hold of two old J&J custom barrels.

[AGD]

All,

Now I just want to point out to everyone that Glenn and I are having a very pointed discussion about the subject at hand. We are both presenting facts, opinions and points of view.

It is refreshing to have such a discussion without it breaking down into name calling and disregarding the others opinions. This is why I love Glenn, he is a no BS guy. Doesn't take it and as importantly doesn't give it.

This type of discussion represents what Deep Blue is suposed to be all about.

Thanks Glenn.

Tom

[AGD]

Ok back to the battle,

Glenn, I am purposely leaving the valving air blast thing out of this becasue it's one of the things on the table to be examined at the end.

You do make a point that todays groups may in fact be closer due to the better propellent, aka compressed air, than a decade ago. I also thought about why you may be getting a full powder scrape off the inside of the barrel. It could be because todays balls are much rounder than 10 years ago. I know they could be off by 20 thou in 92.

I will absoulutely give you the valve tuning issue if it concerns tighter velocity spread out the barrel. If it affects down range flight you would have to explain that to me.

AGD

[than205]

Tom,
Since we are considering that paintball production has evolved to the point where they are much "more round".
I'm curious to persue the "ball distortion" issue. Wouldn't we just want to do the powder test with a "very" large bore barrel to find out whether or not the paintball distorts to fit the barrel? Or does it bounce around? Or what ever....

[Cristobal]

Originally posted by than205
Tom,
Since we are considering that paintball production has evolved to the point where they are much "more round".
I'm curious to persue the "ball distortion" issue. Wouldn't we just want to do the powder test with a "very" large bore barrel to find out whether or not the paintball distorts to fit the barrel? Or does it bounce around? Or what ever....

It would be interesting to do more testing to see if the results Paladin got are consistent across the board. Based on the results described in AGD's tech tip on barrel sizing, I'm betting that the ball will only expand to a point and that in a very large bore barrel the ball would bounce back and forth.

From the tech tip:
If the barrel is too big, the ball ricochets back and forth down the tube. We used to say it looked like Zebra stripes in there. Hence big barrels do NOT create an "air bearing". Barrels that are too small scrape most of the powder off and this creates excessive FRICTION. Tighter barrels that were too long were found to slow the balls down due to this friction. In other words, when you cut these barrels down, velocity went up. Remember the 8-10" acceleration distance, these barrels were 14" long and unported.

[hitech]

Tom,
Did you ever photograph any paintball flights that were fired from a barrel with "paint" in it? I think we have all observed enough evidence to believe that "paint" in the barrel adversely effects accuracy, unless you are trying to curve it around a tree.

[Paladin]

Originally posted by AGD
All,

Now I just want to point out to everyone that Glenn and I are having a very pointed discussion about the subject at hand. We are both presenting facts, opinions and points of view.

It is refreshing to have such a discussion without it breaking down into name calling and disregarding the others opinions. This is why I love Glenn, he is a no BS guy. Doesn't take it and as importantly doesn't give it.

This type of discussion represents what Deep Blue is suposed to be all about.

Thanks Glenn.

Tom

Ditto, what Tom just said!! ^ Thank you too. Always a pleasure !!!

Now, I have a couple more tests that I want to try to duplicate today before I get into the "goggles on" envrinment of Tom's next post.

Quik Question: Anyone, that is following this thread, have any experience with or a connection to freefall parachuting, aka Skydiving ??
If so, try following some round and/or not so round objects in feefall sometime. Makes for some very interesting observations regarding the effects of air flow over various objects and their shape orientation to the line of flight. Especially at the transition from acceleration to achieving "terminal velocity" speeds ranging from 150 to 300 FPS. I haven't done any serious jumping in many years and I sure wish I had some video of some of the stuff we did.

[bjjb99]

Test #114 Analysis

Analysis of the test #114 image

I am calling the first image of the ball outside the barrel "position 1". "Position 0" is inside the barrel.

Front view spin:
Position 1: 36.3 degrees
Position 2: 24.6 degrees
Position 3: 14.4 degrees
Position 4: Washed out
Average spin: 11.0 degrees per strobe flash, spin vector away from camera, "top-spin" from the shooter's point of view.

Underside view spin:
Position 1: -3.2 degrees
Position 2: -22.1 degrees
Position 3: -36.0 degrees
Position 4: Washed out
Average spin: 16.4 degrees per strobe flash, spin vector down, "left-spin" from the shooter's point of view.

Axial spin is negligible.

Based on the measured spin directions, the Magnus effect should cause the ball to drift downwards and towards the camera. Here are the position measurements from the test #114 image.


Front view position of ball:
Position 0: 29 mm above string (bottom of ball)
Position 1: 30 mm above string (bottom of ball)
Position 2: 31 mm above string (bottom of ball)
Position 3: 32 mm above string (bottom of ball)
Position 4: Washed out

Underside view position of ball, "towards the camera" and "in front of the string" is "down" in this portion of the image because of the mirror used to image the underside:
Position 0: Indeterminate. Ball does not appear to line up with barrel exit.
Position 1: 9 mm in front of string (front surface of ball)
Position 2: 9 mm in front of string (front surface of ball)
Position 3: 7 mm in front of string (front surface of ball)
Position 4: Washed out

The ball actually rises slightly and moves away from the camera. The Magnus effect predicts exactly the opposite of what we observe in test #114. There is an anti-Magnus effect that rears its head for smooth spheres, but its effect is generally weaker than the forces predicted by the Magnus effect. Given that test #101 showed that the Magnus effect resulting from a spin of 15 degrees per strobe flash was resulted in too small a deviation to measure with the scanned images provided, and given that the spin in test #114 is comparable in magnitude to the spin in test #101, it is reasonable to conclude (without having to go through all the math) that the deviation imparted by the Magnus effect in test #114 is also too small to measure in the scanned image provided.

Not only is the deviation imparted by the Magnus effect in test #114 too small to be measured, but the deviation is also predicted to be in the opposite direction of the measured deviation!

The rise of the ball as measured in the front view image appears linear (to within measurement error), which seems to indicate that it is either a result of not quite perfect alignment of the barrel and string, or an initial upwards "kick" that occurred just as the ball exited the barrel.

The motion of the ball away from the camera is not quite as linear, but is still reasonably so to within measurement error. The ball may have acquired a slight "kick" away from the camera as it exited the barrel.

What could cause a ball to be kicked slightly in a direction as it exits the barrel? I suppose slight kick could be imparted to the ball as a result of the differential pressures encountered from a nonuniform air release. I took a look at the smoke*.tif images to see if I could detect any nonuniformity in the way the gas escaped, but I couldn't make any conclusions from those images.

Based on tests 101 and 114, I think that the Magnus effect is not what causes the shot-to-shot inconsistency seen in modern markers; the spin resulting from a barrel not specifically designed to induce spin (i.e. Flatline, etc.) is not sufficient to deflect the ball from its normal course. The inconsistency may be the result of nonuniform release of air behind the ball as it exits the barrel. In normal gameplay, pockets of air turbulence may be a factor.

BJJB

[Kip Walker]

if acuracy is decided by how the liquid in the ball spins or dosen't spin then to get the fill to spin would be to solve a great problem. Mabey making the paint thicker would help the fill to spin when the shell spins. Then the fill would spin with the shell and we could just start rifling the barrels like actual rifles.

[AGD]

BJ,

NICE JOB!! Good analysis. Ok so NOW we are seeing real data that points in a direction, it just seems that the direction is not what everyone expected. So is the way of science.

So please lets assume for a second that this 114 data generaly represents what's going on with paintballs. (I happen to know it does)

The next claim is that maybe the ball is kicked sideways right out of the barrel. If this were true you would expect to see it deviate in one direction and that direction would be significantly increased in the second camera trap. If you look at the picture called "3D interpretation" you will see the balls position plotted as relative movement from one pic to another. If you look at the first position in the second trap (flash #6) you will see that the ball trended LEFT from the #5 flash postion but it hits WAY RIGHT at the final target backdrop.

So if we interpret the data correctly the ball "S" curved in flight. This is not consistent with a ball knocked off course at launch.

We are getting better lets stick to it.

AGD

[Redkey]

Originally posted by AGD


So please lets assume for a second that this 114 data generaly represents what's going on with paintballs. (I happen to know it does)

AGD

So, the conclusion based on BJJB99s nifty numbers work is that spin does not have an effect on accuracy? And... this conclusion is supported by all the other unseen data?

I don't entirely agree with that statement... but, I cannot disprove it. So I'll assume it's true until it can be proved otherwise.

So... where does that leave us? Why don't balls fly straight? Obivously there is something happening during the balls flight to cause it to wander. They had the same problem a few hundred years ago with muskets... everyone knows how they solved that problem.

Have the same accuracy tests been tried with nylon balls? Assuming the solid ball is homogeneous... that should remove any inconsistancies associated with the paintball. From my playing around with shooting nylon balls I found they hooked like crazy. I might have been shooting a bit hot which could contribute to the inaccuracy. Have you seen similar results with nylon balls?

Why is a paintball shot from a barrel coated with paint from a broken ball so inaccurate? Is there spin? Does the paint coating the ball cause it to hook?

What was the flash *duration* on the strobes used for your photographs?

again... more questions than answers. Sorry.

[bjjb99]

Originally posted by Redkey

So, the conclusion based on BJJB99s nifty numbers work is that spin does not have an effect on accuracy? And... this conclusion is supported by all the other unseen data?

I think the conclusion is more along the lines of "the levels of spin seen in the test 101 and test 114 data are not sufficient in and of themselves to affect accuracy to the magnitude seen in those tests." This is not to say that spin has no effect on accuracy; the Flatline barrel turned on its side clearly shows that spin does affect accuracy. But then the level of spin induced by a Flatline barrel is (I assume) significantly greater than what tests 101 and 114 show.

Originally posted by Redkey

Why is a paintball shot from a barrel coated with paint from a broken ball so inaccurate? Is there spin? Does the paint coating the ball cause it to hook?

I think it may be a combination of spin and a nonuniform coating of fill on the outside of the ball which causes the horrible accuracy one sees when firing a shot from a paint-filled barrel. The spin would likely be greater than that seen in tests 101 and 114 so we'd be closer to the Flatline barrel regime in terms of shot curvature. The nonuniform coating of paint on the ouside of the paintball might result in an effect similar to golf ball dimples, increasing the turbulent flow and thus magnifying the effects of spin even more. Of course, this is all guesswork on my part.

Originally posted by Redkey

What was the flash *duration* on the strobes used for your photographs?

The ball from test 101 appears very round in flight, perhaps only a pixel or two "longer" in the direction of flight. Assuming this is from the flash duration, it amounts to about 1 mm of travel during the flash exposure. At 280 fps, we get 1 mm of travel in about ten microseconds. Thus I'm betting that the strobes are around 10 microseconds in duration (or possibly a bit faster if some of the ball elongation resulted from a failure to recover from possible deformations during firing).

BJJB

[bjjb99]

Originally posted by AGD

The next claim is that maybe the ball is kicked sideways right out of the barrel. If this were true you would expect to see it deviate in one direction and that direction would be significantly increased in the second camera trap. If you look at the picture called "3D interpretation" you will see the balls position plotted as relative movement from one pic to another. If you look at the first position in the second trap (flash #6) you will see that the ball trended LEFT from the #5 flash postion but it hits WAY RIGHT at the final target backdrop.

So if we interpret the data correctly the ball "S" curved in flight. This is not consistent with a ball knocked off course at launch.

What is the vertical and horizontal scale (preferably in inches per pixel) used in the file labeled 114axis.TIF? If my measurements from the in-flight shots of test 114 are reasonably correct, and if I'm applying them correctly to 114axis.TIF, then the "WAY RIGHT" you're talking about amounts to about 2.25 inches of deviation from the point of aim at the final target backdrop.

A total horixontal in-flight deviation of less than 2.5 inches might be explained away by unstable air, either in the form of density gradients or residual air currents from people having moved through the test area prior to testing.

BJJB

[Paladin]

Originally posted by AGD
BJ,

So if we interpret the data correctly the ball "S" curved in flight. This is not consistent with a ball knocked off course at launch.

We are getting better lets stick to it.

AGD

Since the ball seems to have a rotation to the right, it makes sense that it would have "S" curved in flight even if it had gotten a little "kick" to the left as it exited the barrel. Based on the orientation of the seem of the ball to the line of flight, as seen in test #1:01 any muzzle blast could easily move it to the left a bit and then allow the rotation to move it back to the right.