[brycelarson]

nickp, on Aug 25 2009, 03:47 PM, said:

Wont this cause a decrease in acuracy? I know with underboaring this will still happen but not as much so overboaring is more acurate?

the fluctuation in shape is so small that it doesn't cause a measurable change in accuracy. I mean, the largest underbore I've had is something along the lines of .007 or .008. That's a couple of human hair thicknesses.

Again, it's about scale. It's possible that a 690 ball through a 670 back would cause such paint deformation that there would be a negative effect. I don't know.

[Leftystrikesback]

It actually doesn't change shape much at all. I did a finite element analysis on it in a thread about 6 months ago and it shows changes in roundness of something like 10^-5 inches.

The boundary layer of air (the uniformly flowing region) separates from a sphere and turns into a turbulent wake well before the 90 degree line (80 degrees in laminar flow, I think something like 65 in turbulent), so a small deformation at the 90 degree line would not affect the turbulence or wake much at all. It seems to me that the paintball's seam would do more to affect the turbulence / wake because based on it's orientation, it could affect the point of BL separation.

[MNpaintball]

another question for you punkworks guys, but i don't know if it has been answered yet...

Can the length of a barrel effect the FPS consistency while shooting? especially when underboring, does the length of the barrel effect this?
i was wondering if friction was a factor between the paintball and barrel, and if the paintball would ever get "caught up" on the barrel if it was a little longer.

is this a simple NO?

thanks

[MNpaintball]

anyone?

[brycelarson]

MNpaintball, on Aug 25 2009, 04:29 PM, said:

Can the length of a barrel effect the FPS consistency while shooting? especially when underboring, does the length of the barrel effect this?
i was wondering if friction was a factor between the paintball and barrel, and if the paintball would ever get "caught up" on the barrel if it was a little longer.

you're actually asking two questions here.

first, there seems to be a slight correlation between barrel length and consistency. It looks like shorter barrels are more consistent. the two piece barrels were a touch more consistent than the one-piece barrels. So, if I had to guess what the most consistent barrel was - it would be a barrel with between 6 and 12" of underbored control bore with between 2 and 4" of overbored, ported end after that. It looks like the shorter the part of the barrel in which the ball is accelerating the more consistent.

to the second part of the question - yes, at some point the barrel will start to slow the paintball. the 16" barrel shot just a bit less efficiently than the 14" barrel - in a one piece constant bore situation. This means that somewhere between 14" and 16" the friction on the ball starts to slow it down before it exits the barrel.

[MNpaintball]

ok.
so it seems that the optimal set up for a barrel would be a freak kit with a .682 or .679 bored back with a tip that made the total length around 10"? that is, if there ever was an optimal barrel set up.

another question then, could you put into perspective how much or little these air efficiencies really are?
like a 5% gain in efficiency from overboring to underboring? 10%?

i'm just curious in what you guys have found in your very numerous tests with barrels...

[brycelarson]

MNpaintball, on Aug 25 2009, 09:45 PM, said:

ok.
so it seems that the optimal set up for a barrel would be a freak kit with a .682 or .679 bored back with a tip that made the total length around 10"? that is, if there ever was an optimal barrel set up.

another question then, could you put into perspective how much or little these air efficiencies really are?
like a 5% gain in efficiency from overboring to underboring? 10%?

i'm just curious in what you guys have found in your very numerous tests with barrels...

I'll pass this along to a person better with physics than me. We saw something along a 20-25 fps change from largest bore to smallest bore. That's out of aprox 275 fps - so we're looking at 10% increase in speed - at the highest end of things.

Sorry, I'm not remembering right now - can someone chime in here - that equates to how much energy savings?

oh, and the freak is prob a bit shorter than optimal for control bore length. the one piece barrels were slightly more efficient. I've got a possible test in the future that would give a better answer about what the optimal control bore length would be. I'm going to go out on a limb and say that it's going to be more like 10"

This post has been edited by brycelarson: 25 August 2009 - 10:48 PM

[Leafy]

back to the discussion about control length and porting. In the AGD studies I swear TK said something about the ported section of the barrel being practically useless except for reducing sound, I'd like to disagree, ever try shooting just a back? So the ball must still be accelerating even in the ported section of the barrel.

[cockerpunk]

Leafy, on Aug 25 2009, 11:09 PM, said:

back to the discussion about control length and porting. In the AGD studies I swear TK said something about the ported section of the barrel being practically useless except for reducing sound, I'd like to disagree, ever try shooting just a back? So the ball must still be accelerating even in the ported section of the barrel.

it is. in out testing the CP backs showed significantly less FPS then the back plus a 2 inch front which was ported.

[Leafy]

cockerpunk, on Aug 26 2009, 12:13 AM, said:

Leafy, on Aug 25 2009, 11:09 PM, said:

back to the discussion about control length and porting. In the AGD studies I swear TK said something about the ported section of the barrel being practically useless except for reducing sound, I'd like to disagree, ever try shooting just a back? So the ball must still be accelerating even in the ported section of the barrel.

it is. in out testing the CP backs showed significantly less FPS then the back plus a 2 inch front which was ported.

and I experienced this on a gun that most of us assume to have a high breach pressure, 98c. It was impossible to get the velocity over 220 fps but it seemed to be very consistent at that.

[Leftystrikesback]

brycelarson, on Aug 25 2009, 08:46 PM, said:

I'll pass this along to a person better with physics than me. We saw something along a 20-25 fps change from largest bore to smallest bore. That's out of aprox 275 fps - so we're looking at 10% increase in speed - at the highest end of things.

From this test data the largest bore (.696) shot 9 fps slower than the smallest bore (.682). 9 / 286 = 3.1% slower. But the biggest difference in efficiency was actually between the smallest bore and the bore that matched the paint (.686) with a difference of 11 fps. 11 / 286 = 3.8% slower.

That's just velocity change, the change in efficiency is calculated from the energy used like bryce said. Energy is proportional to velocity squared so the biggest difference in efficiency is between the paint-bore match and the underbore at ((286^2) - (275^2)) / (286^2) = 0.075 So paint to bore match is 7.5% less efficient than underboring.

Between Overbore and underbore, the overbore is 6.2% less efficient.
((286^2) - (277^2)) / (286^2) = 0.062

Obviously all those values are from limited test data with some error. I used the data from barrels of the same length so that the only differences being compared are bore size. There are larger drops in efficiency when you combine overboring with say a really short barrel.


Edit: Haha wow there were 3 posts durring the time it took me to do that. sad for me.

Quote

in out testing the CP backs showed significantly less FPS then the back plus a 2 inch front which was ported.

This is interesting. Just goes to show that as long as there is some pressure difference in the barrel the ball will keep accelerating.

This post has been edited by Leftystrikesback: 25 August 2009 - 11:23 PM

[Leafy]

Leftystrikesback, on Aug 26 2009, 12:18 AM, said:

brycelarson, on Aug 25 2009, 08:46 PM, said:

I'll pass this along to a person better with physics than me. We saw something along a 20-25 fps change from largest bore to smallest bore. That's out of aprox 275 fps - so we're looking at 10% increase in speed - at the highest end of things.

From this test data the largest bore (.696) shot 9 fps slower than the smallest bore (.682). 9 / 286 = 3.1% slower. But the biggest difference in efficiency was actually between the smallest bore and the bore that matched the paint (.686) with a difference of 11 fps. 11 / 286 = 3.8% slower.

That's just velocity change, the change in efficiency is calculated from the energy used like bryce said. Energy is proportional to velocity squared so the biggest difference in efficiency is between the paint-bore match and the underbore at ((286^2) - (275^2)) / (286^2) = 0.075 So paint to bore match is 7.5% less efficient than underboring.

Between Overbore and underbore, the overbore is 6.2% less efficient.
((286^2) - (277^2)) / (286^2) = 0.062

Obviously all those values are from limited test data with some error. I used the data from barrels of the same length so that the only differences being compared are bore size. There are larger drops in efficiency when you combine overboring with say a really short barrel.

so does that 6% go directly to shot count, like if I get 1900 shots off my protege with a wicked over bored barrel that I'd get 2014 shots a 114 shot increase? Or am I not understanding?

[brycelarson]

Leafy, on Aug 25 2009, 11:21 PM, said:

so does that 6% go directly to shot count, like if I get 1900 shots off my protege with a wicked over bored barrel that I'd get 2014 shots a 114 shot increase? Or am I not understanding?

yup that should be right.

[Leafy]

holy crap.

[MNpaintball]

Leftystrikesback, on Aug 25 2009, 11:18 PM, said:

From this test data the largest bore (.696) shot 9 fps slower than the smallest bore (.682). 9 / 286 = 3.1% slower. But the biggest difference in efficiency was actually between the smallest bore and the bore that matched the paint (.686) with a difference of 11 fps. 11 / 286 = 3.8% slower.

That's just velocity change, the change in efficiency is calculated from the energy used like bryce said. Energy is proportional to velocity squared so the biggest difference in efficiency is between the paint-bore match and the underbore at ((286^2) - (275^2)) / (286^2) = 0.075 So paint to bore match is 7.5% less efficient than underboring.

Between Overbore and underbore, the overbore is 6.2% less efficient.
((286^2) - (277^2)) / (286^2) = 0.062

damn you're smart.

[Pearlsea]

This should be stickied :|

[Leftystrikesback]

Leafy, on Aug 25 2009, 09:21 PM, said:

so does that 6% go directly to shot count, like if I get 1900 shots off my protege with a wicked over bored barrel that I'd get 2014 shots a 114 shot increase? Or am I not understanding?

Good question... the simple answer is yes.
If you want to get more complicated it's less than that because you can't use all the energy stored in your tank (ya know, you can't shoot below a certain pressure and all that), but still a close approximation.

Leafy said:

holy crap.

Yeah it doesn't seem so trivial when you put numbers to it huh? I didn't really realize how significant it was either until I did the math just now. That $30 .682 CP back practically pays for itself.

[kenzie]

great video helps alot

[Troy]

I'm wondering when we will see a Punkworks edition Stiffi or CP built to Bryce's specs...

[brycelarson]

Troy, on Aug 26 2009, 06:55 AM, said:

I'm wondering when we will see a Punkworks edition Stiffi or CP built to Bryce's specs...

never a PunkWorks edition. We want to maintain our independence. If we work with a company and put our name on a barrel - then we certainly have removed all barrel testing from what we can do w/o bias.

As to someone building a barrel to what I think are the optimal specifications - sure. This information is all public. If a barrel manufacturer happens to find what we do interesting enough to spend half an hour on the phone - then they're going to get some ideas from me. If they choose to implement those ideas - then I'll test the barrel and see if it really is better. If it is - I'll say so, if it's not - then I will tell them that - but if PunkWorks name is on it - then we're stuck.

We are working on a program to verify manufacturer claims. We won't be endorsing the product - but we are talking about allowing companies to use our name. This would only be if we can replicate the results they want to claim. There would be no exchange of goods or money - simply our agreement that what they're claiming is a real, repeatable result.