Paintball Spin Physics - Getting to the final Answer

[AGD]

(pics here) 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.

original thread

[nippinout]

Tom, could you elaborate on the ball exploding pictures?

Thanks.

Moving on...

The hypotheses are a great way to start. I suggest destroying each one until proven one way or the other.

pbJosh proposed that spin is the only contributing factor for paintball inaccuracy. As posted earlier by Tom, "The testing we have done shows that the small induced spin on paintballs does not correlate with where it hits the target when the spin is below 6000 rpm."

To refute the statement about spin, we only have to prove that their is another effect on accuracy.

Tom also found that any spin induced, the ball's spin will slow down after leaving the barrel. But the spin rate of the shell and fill will equalize. Tippmann was able to show the spin does have an effect. However, the spins were on different axes. The AGD spin was spinning on the barrel axis and the Tippmann spin perpindicular to AGD's.

The AGD spinning didn't affect the trajectory due to the spin on the path the ball was taking.

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

Otherwise, external of the barrel, spin seems to have little effect. Internally, spin may play a large factor. Rolling friction and sliding friction are two different beasts. Static friction is a higher value than kinetic friction. It takes a larger force to move an object than to keep an object IN motion. In open bolt guns, the ball will be in motion while the valve is opening. In closed bolt guns, the ball is waiting to be propelled.

At high rates of fire a closed bolt may behave like an open bolt, but the ball will still be either waiting, or already in motion. But how much of a role does static vs. kinetic friction play?

Glenn stated that when breech loading paintballs, he was able to see a difference in velocities with different arrangements of the ball. With the 'fattest' placement coming from the seams and higher velocity. The arrangement of the seams would affect velocities. The velocities would affect accuracy. Therefore, the seams do have an effect on accuracy.

Tom also did a test with seams. His test used old school Desenex foot powder and found that a bore that only leaves two streaks left by the seams gives the best shot to shot consistency.

Although we would have the best consistency by placing the ball perfectly, we cannot. So for the best 'real world' consistency, we go with the Desenex solution. Both findings depend on the bore of the barrel. Barrels DO have a role in accuracy.

To test for distortion, couldn't we perform a modified Desenex test? Do a Desenex test, but with the same barrel do a blow test. If you could blow a ball or even push it leaving the same streaks, it would disprove the distortion of the paintball. In the Desenex test, if the ball did distort, it would have scraped all of the powder out.

Glenn's findings and Tom's findings refute eachother. Tom found that too much friction was a bad thing. Is a full ball/barrel seal too much friction? This would be more friction than just two points, but their is less air sneaking past the ball and doing more work on the paintball.

I'm sleepy. More thinking after I sleep.

Good discussion though!

[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.

[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

[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

[314159]

Re: Paintball Spin Physics - Getting to the final Answer

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.

[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

[314159]

Re: RE PBjosh

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)

[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

[ShooterJM]

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

[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.

[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

[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)-

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.

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

[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

[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