[brycelarson]

https://docs.google....cW1yWlVpRDVKMnc

once again we shoot multiple bore sizes - and yes, underboring too much makes things shoot crappy.

This post has been edited by brycelarson: 23 September 2012 - 05:35 PM

[rntlee]

Well, as this is a rabbit trail I think I caused, I guess I better comment.

I think Bryce, the point you're making here is this: A high degree of under-boring is a know cause of aberrant accuracy, and this aberration is present in the test you just completed with the somewhat poor marbs. Therefore, paint grade doesn't actually obscure barrel-induced effects.

I agree to a point. A high degree of under-bore will add obscene amounts of spin to the paintballs...this is the cause of the increased shot spread, of course. From my own testing, these are the conclusions i have come to regarding shot spread:
The two largest forces affecting shot spread are paintball surface-induced asymmetric boundary layer separation, and spin-induced asymmetric boundary layer separation. These two forces both act on the balls during flight to the target, but the total increase in shot spread isn't an aggregate of the two forces. They interact in a more complex way. The surface-induced forces are generally much larger than spin-induced forces (excepting very high rates of spin), and lower rates of spin-induced forces CAN be almost "absorbed" (for lack of a better word) into the surface-induced forces. I noted this during my short obsession with patching paint. Patched paint from a smooth-bore only shoots tighter groups if the paint is free of surface imperfections. Poorer paint will shoot similar groupings whether patched or not. I have also documented (controversially ) incremental increases in shot spread correlating to bore size that Punkworks hasn't replicated in your own testing. Perhaps it's my obsession with using only the best performing paint I can obtain, idk.

Anyway, these differences aren't apparent with anything other than high performing paintballs. What do I mean by high performing? I've shot dozens of tests myself, and I have a benchmark that I apply to the paint I use. I have to be able to shoot a 5" vector at 80' with it for me to bother completing a test with it. Tests are a lot of work and I just don't want to loose any possible subtle results. I'm a bit obsessive that way. I don't have a lot of 100' data, but I'd guess that good paint should shoot a vector of no more than 7"-9" at that distance. There's considerable "noise" to sift out if your paint is delivering 14" vectors.

Nevertheless, the possible muzzle effects that the new barrel was designed to mitigate are much subtler than the surface-induced forces poor paint can generate. Why not eliminate as much noise as you can?

[Troy]

brycelarson, on 21 September 2012 - 08:54 AM, said:

https://docs.google....cW1yWlVpRDVKMnc

once again we shoot multiple bore sizes - and yes, underboring too much makes things shoot crappy.

What kind of marker was this on? Just interested in whether these observed effects were on a poppet or a spool valve marker, that's all.

[Troy]

rntlee, on 23 September 2012 - 08:02 PM, said:

A high degree of under-bore will add obscene amounts of spin to the paintballs.

I'm wondering how you reached this conclusion. Is it your theory that because the SD of the velocity is so similar to other bores that speed fluctuations couldn't account for the added decrease in accuracy, alone, so the only thing left for it to be is some kind of induced spin? Or is there high speed camera footage out there somewhere showing an increased amount of spin from an underbore?

I think you have a reasonable hypothesis (and I can't come up with a better one), but I would like to see a bit more evidence before I conclude that spin is the culprit. Of course, I could just be ill-informed... if there is some other data that you are drawing from I would be happy to revise my beliefs.

Perhaps we can get PW to get some high speed footage of the ball coming out of an extreme under bore to confirm?

[drg]

Troy, on 23 September 2012 - 10:06 PM, said:

rntlee, on 23 September 2012 - 08:02 PM, said:

A high degree of under-bore will add obscene amounts of spin to the paintballs.

I'm wondering how you reached this conclusion. Is it your theory that because the SD of the velocity is so similar to other bores that speed fluctuations couldn't account for the added decrease in accuracy, alone, so the only thing left for it to be is some kind of induced spin? Or is there high speed camera footage out there somewhere showing an increased amount of spin from an underbore?

I think you have a reasonable hypothesis (and I can't come up with a better one), but I would like to see a bit more evidence before I conclude that spin is the culprit. Of course, I could just be ill-informed... if there is some other data that you are drawing from I would be happy to revise my beliefs.

Perhaps we can get PW to get some high speed footage of the ball coming out of an extreme under bore to confirm?

I believe they already did this and published some spin numbers.

[Troy]

drg, on 23 September 2012 - 10:33 PM, said:

Troy, on 23 September 2012 - 10:06 PM, said:

rntlee, on 23 September 2012 - 08:02 PM, said:

A high degree of under-bore will add obscene amounts of spin to the paintballs.

I'm wondering how you reached this conclusion. Is it your theory that because the SD of the velocity is so similar to other bores that speed fluctuations couldn't account for the added decrease in accuracy, alone, so the only thing left for it to be is some kind of induced spin? Or is there high speed camera footage out there somewhere showing an increased amount of spin from an underbore?

I think you have a reasonable hypothesis (and I can't come up with a better one), but I would like to see a bit more evidence before I conclude that spin is the culprit. Of course, I could just be ill-informed... if there is some other data that you are drawing from I would be happy to revise my beliefs.

Perhaps we can get PW to get some high speed footage of the ball coming out of an extreme under bore to confirm?

I believe they already did this and published some spin numbers.

I know they did it for the Apex, and some of the back spin bolts, but I'm not aware of a severely underbored barrel that they've tested in the same manner. Like I said though, I could be missing something.

[brycelarson]

drg, on 23 September 2012 - 10:33 PM, said:

I believe they already did this and published some spin numbers.

Correct. All barrels produce some spin in a random direction at lower RPM. Heavily underbored barrels (.007+) produce a much higher rate of spin - also in random directions. The random spin direction most certainly plays a part in the inherent inaccuracy of paint.

And yes, Lee - I think you're smart to really dig into paint quality and control that for your tests. We simply made a methodology choice long ago that the results of our tests needed to be applicable to everyday play. In this case we shot the field paint at the largest indoor facility (actually three facilities withing a couple of months) in the area. This is the paint that %75 of the people playing during the winter here are going to be shooting. We have never discounted that some systems might have certain effects with a very highly selected paint - we just have chosen not to do that for our tests.

It was a BL Protege (poppet)

We actually had a certain manufacturer tell us that in order to really see how well their product worked we needed to hand measure and sort the paint then only use balls that were +/- .002 and as round as possible. We simply refused. Until I can buy that paint by the bag then the product has no effective benefit to me.

[Troy]

brycelarson, on 24 September 2012 - 07:07 AM, said:

Heavily underbored barrels (.007+) produce a much higher rate of spin - also in random directions.

Awesome, but how do we know this? Not trying to be a PITA, but I, don't remember there being a test that confirmed this.

[brycelarson]

Troy, on 24 September 2012 - 07:18 AM, said:

brycelarson, on 24 September 2012 - 07:07 AM, said:

Heavily underbored barrels (.007+) produce a much higher rate of spin - also in random directions.

Awesome, but how do we know this? Not trying to be a PITA, but I, don't remember there being a test that confirmed this.

sorry - forgot to mention that. We used HS video.

http://www.punkworks...x.php?p=7&id=39

This post has been edited by brycelarson: 24 September 2012 - 07:25 AM

[Troy]

brycelarson, on 24 September 2012 - 07:24 AM, said:

Troy, on 24 September 2012 - 07:18 AM, said:

brycelarson, on 24 September 2012 - 07:07 AM, said:

Heavily underbored barrels (.007+) produce a much higher rate of spin - also in random directions.

Awesome, but how do we know this? Not trying to be a PITA, but I, don't remember there being a test that confirmed this.

sorry - forgot to mention that. We used HS video.

http://www.punkworks...x.php?p=7&id=39

Excellent, thanks. The data from that video meshes nicely with the data from this test, showing ~.03 underbore being the best.

This post has been edited by Troy: 24 September 2012 - 09:20 AM

[cockerpunk]

yeah, i think we need to look back at sabots again. between this and the 'cuda testing, i think it shows that spin, combined with minor aerodynamic imperfections is the really the fundamental problem with accuracy. in that with no spin, even a relatively poor aerodynamic ball can shoot reasonably straight, or even with a nominal amount of spin, a near perfect ball can fly reasonably straight.

[cockerpunk]

i also like this test because we actually did prove something. unlike every other accuracy test that basically comes up "no difference" here we actually saw a real difference, if a bad difference.

[Snipez4664]

cockerpunk, on 24 September 2012 - 09:33 AM, said:

yeah, i think we need to look back at sabots again. between this and the 'cuda testing, i think it shows that spin, combined with minor aerodynamic imperfections is the really the fundamental problem with accuracy. in that with no spin, even a relatively poor aerodynamic ball can shoot reasonably straight, or even with a nominal amount of spin, a near perfect ball can fly reasonably straight.

must figure out where that spin come from

Working hypothesis was sabot improvement real

If sabot real, seem most likely mitigates muzzle effects

possible with fixed barrel?

constrain ball while assuring all air vented

CFD barrel tip, where turbulent zone

ensure max turbulence inside fluting

try shoot barrel now








faulty line of logic maybe in bold.

sabot prevent interaction with walls, simulate type air bearing? like rntlee see in overbore accuracy?

Back to tom kaye and foot powder

more things change more things remain

[cockerpunk]

yeah i agree that is the flaw in the logic. i think the 'cuda testing pounds a pretty hefty nail in the coffin of muzzle effects. or at least muzzle effects that design can solve. i certainly can't think of much that wasn't done to the muzzle of that barrel.

so that, combined with this test that confirms out earlier hypothesis about spin an accuracy in extreme underbores, points back at sabots reducing spin.

[Snipez4664]

disagree

would need to use sabot'd paint as control, on any given paint quality, to test elimination of initial effects (spin, trajectory)

If sabot not make improvement with given paint quality, test cannot reach conclusions




agree that spin, rather than initial trajectory is problem

but not useful statement for design

where spin come from

how sabots stopping it

[cockerpunk]

i think we should repeat the sabot testing under high speed, using better paper towels (rntlees were solid, mine were disintegrating), to see if indeed spin is being killed in the first place.

[Snipez4664]

very interesting test, agree.

can make conclusions with both good and bad paint

rntlee, were the sabots folded around sides of balls to prevent bore contact?

I think not enough clearance for that

[spankopotomous=paintball]

Snipez4664, on 24 September 2012 - 12:51 PM, said:

disagree

would need to use sabot'd paint as control, on any given paint quality, to test elimination of initial effects (spin, trajectory)

If sabot not make improvement with given paint quality, test cannot reach conclusions




agree that spin, rather than initial trajectory is problem

but not useful statement for design

where spin come from

how sabots stopping it

Ug


Snipez must be working or on phone

Type like caveman

Ug

He go club woman for snu snu now

/jk

[Troy]

^^^That's funny.

Btw, I wanted to throw out some random speculation...

If we think that barrel induced spin is a cause of inaccuracy, do you think this could be the reason that I saw an INCREASE in accuracy in paint that was slightly oblong in my test? I'm thinking if the paint "found a home" in the barrel with the minor axis perpendicular to the barrel, the underbore could have prevented it from spinning in the barrel.

This post has been edited by Troy: 24 September 2012 - 03:59 PM

[cockerpunk]

Troy, on 24 September 2012 - 03:58 PM, said:

^^^That's funny.

Btw, I wanted to throw out some random speculation...

If we think that barrel induced spin is a cause of inaccuracy, do you think this could be the reason that I saw an INCREASE in accuracy in paint that was slightly oblong in my test? I'm thinking if the paint "found a home" in the barrel with the minor axis perpendicular to the barrel, the underbore could have prevented it from spinning in the barrel.

yeah, that is my thoughts as well.

but as an increase in useable accuracy, i don't think we have seen that in any testing.