Last of the Salzburg Clan
and again, for a safety check, if 20 shots doesn't give you a good average of the velocity, then we are all VERY VERY VERY unsafe right now. that means the 3 to 8 shots you fire over the chrono is not a good enough sample to establish the mean, and thus very unsafe ... by your definition of what is needed to compute an average. we should be shooting hundreds of shots over the chono to get a good average by your definition in this thread.
Last edited by cockerpunk; 07-30-2013 at 03:15 PM.
1. the min to max diameter of a paintball, even a good one, can vary by as much as .020" inches. not kidding
2. the actual size of the paintball isn't the important part of its interaction with the barrel. the interaction with the barrel be summed up with two competing values ... the friction withe barrel, and the quality of the seal with the barrel.
now lets break that down:
friction: friction is obvious with the barrel, computed with the normal force (compression in this case) and the coefficient of friction. the coefficient of friction is largely irrelevant because it is a term in very computation, and is very similar between brands, so we can effectually ignore it. this leaves friction as essentially only related to the force of compression acting on it from the barrel. essentially, the amount the ball has to change to fit in the barrel. this is related to size, but also to orientation of the ball, and out of roundess of the ball.
seal quality: this is a function of the area gap between the footprint of the ball, and barrel. this is related to size, but also to orientation of the ball, and out of roundess of the ball.
so, the ratio of these two competing qualities is what determines the performance of a ball/barrel system.
so measuring the ball is largely a waste of time, unless you measure it in relationship to these two things. the blow test measures these two competing forces directly. because the human body cannot produce much beyond a few PSI, and the resualts are clear in terms of friction, this allows us to select the "blow test size" of a paintball. now the actual size as i said is essentially irrelevant, because again, the only thing that matters in this system is those two competing forces, as it is the only set of forces the ball ever sees in the barrel. and since we determine under vs overbore based on the blow test size, the conventions are all correct. blow test your paint, and then move down 3 to 5 thousandths for ideal performance.
Last edited by cockerpunk; 07-30-2013 at 02:59 PM. Reason: spelling
I'm not saying you are right or wrong; I'm just saying the data is incomplete to convince me at this point.
I am sincerely enjoying this thread, and I mean for all of my responses to be respectful and mature. I sympathize, as it is often hard to be on the presentation side of data. I've been there many times. I simply want to discuss the data, not attack it.
this is why i most often refer to paint in "blow test size" not actual physical size. because the blow test functional size is the only one that actually matters.
Do you have a string of 100 shots on a non-breaking-in-gun so that I can re-make my point?
Again, I'd rather do it with your data than mine.
I haven't eyeballed the minimum number of shots needed to get a decent average.
Average and standard deviation are not the same thing. It is entirely possible to arrive at a decent average at some number of shots, but still not have enough shots to get a decent standard deviation.
I am speaking to standard deviation directly.
Again, this point can probably be made if you point me at your data for a longer run of shots.
Just looking at your breaking-in-data which you don't want to accept as valid, but let's look at it anyways:
At shot 512, the STDEV was 7.91, and the average was like 248.
On the other end of the range, shot 447 had STDEV of 11.64, but the average... was 243.
So 25 shots might be good enough for average, but the STDEV varies so much as to not be useful.
Last edited by GoatBoy; 07-30-2013 at 04:20 PM.
"Accuracy by aiming."
Definitely not on the A-Team.
ill give you consistency is a tricky one, if you note in the first test data, two .687 freak inserts shot quite different consistencies ....
The problem I have with this is chambering orientation is completely random. So no matter what method I use for the blow test, I could swing from underboring to overboring (or extreme conditions of either) given the paintball inconsistencies. This is why I stated earlier to get it relatively close, and fire away, hoping the paintball chambering orientation gods are on your side that day.
When you measure the size of a paintball for the purpose of determining a bore size, always measure the seam. That will always be the largest diameter. Any barrel you select at that size will always touch on two points. So, if you physically measure each paintball, you can accurately select ones that are consistently sized. Of course, this depends on the paint being in good condition and round. Any paint that is not round won't work like that but should not be used for testing anyway. You can determine that by measuring the balls at two points on the seam at 90 degree angles from each other. Any measured values that are noticeably different should have that paintball tossed out of the test.
Except for the Automag in front, its usually the man behind the equipment that counts.
athomas: Any given barrel size essentially acts like a go/no-go gage. Fit testing at the seams seems most logical. However, orientation changes could lead to extreme overboring, and paintball inconsistencies could lead to extreme underboring. I would think you would not want to throw out the out of round paint unless you are going to sort your entire supply. As you stated earlier, if you don't account for those few fliers, they could become an issue.
cockerpunk: Do you see any validity to repeating your test, performing your blow test with properly oriented seams, noting that bore size, and then gradually decreasing bore size until you do start to see obvious evidence of underboring causing barrel breaks? Perhaps you could do this with economy, mid, and high level paints from a few different companies. This could lead to a very repeatable procedure of what the average player should do and expect given a certain quality of paint, and the degree of underboring that could be safely used. Do whatever sample size you feel is appropriate for average and standard deviation (I see n=30 tossed around a lot), but I would be more concerned with quality X paint breaks Y balls out of a pod/hopper/bag/case/etc. with Z level of underboring. You may want to show barrel breaks going two or three inserts in the overbore direction as well just to cover everything. I think all this in a single chart, would let each individual decide on consistency, efficiency, and relative risk for their personal preference.
I didn't get a chance to look through all the other data you linked earlier. Maybe you already have this.
Other than that, if you know you have imperfect paint, you need to expect inconsistent shooting. Now you have to deal with it using a method you are comfortable with. Perhaps you should measure a large sample of balls and determine the smallest diameter of contact and use that as your barrel size. Then, every other ball will be using an underbore. Or, do the same using the largest measured diameter, except use an overbore. Personally, I use an "extreme" overbore. I sacrifice efficiency, but my shot consistency is good.
Always having two points of contact is agreed upon, until you start compressing the ball, at which point those two points become larger "point" surfaces, and eventually "line" surfaces around the entire circumference.
Given the previous statement that accuracy is unaffected by consistency up to around 15fps (although a relative statement, I tend to agree with it, because "aiming" inconsistency is a much larger factor), are we really just talking about efficiency? If I recall correctly, any insert in cockerpunk's data was below a 7.5fps st dev. And if consistency leads to nothing more than accuracy, but all inserts produce an acceptable consistency, should we really just be comparing efficiency vs. potential ball breaks?
I can't agree to anything that isn't backed by data, and that includes efficiency.
For average velocity, 20 is probably fine, judging by the data.
For standard deviation in velocity, 20 does not appear to be fine when the possible error in the standard deviation resulting from a sampling of 20 shots is potentially on the same scale as the trend that you were trying to indicate.
I ran some numbers with my own data, I will plug yours in once I figure out which data of yours you're willing to accept. Like I said originally, I looked at the last 100 of your first 500 because the previous shots were probably going crazy. Sure, you'll get an errant shot every now and then. That's what a larger sample is supposed to smooth over. Errant shots, and the probability of hitting a particularly bad run which is not reflective of the overall deviation, either on the + or - side. Shorter runs have a higher probability of showing up.
I did a run of 100 shots, same paint, same barrel, two different guns. (My testing was actually targeting efficiency.) I also generated random numbers with a similar FPS variance. Here's what it looks like:
Window size 10, stdev variance 8.871928-2.936362=5.935566, mean variance 8.400000
Window size 20, stdev variance 6.990783-4.148240=2.842543, mean variance 5.700000
Window size 30, stdev variance 7.515195-4.657092=2.858103, mean variance 2.666667
Window size 40, stdev variance 6.978171-5.118844=1.859327, mean variance 1.750000
Window size 50, stdev variance 6.476457-5.346599=1.129857, mean variance 1.460000
100 shot (mean, stdev) = (284.24, 6.171161343153523)
Window size 10, stdev variance 8.875059-3.335000=5.540059, mean variance 9.800000
Window size 20, stdev variance 8.041177-4.073018=3.968159, mean variance 6.250000
Window size 30, stdev variance 7.793381-4.508485=3.284896, mean variance 5.600000
Window size 40, stdev variance 7.330302-5.196399=2.133903, mean variance 3.600000
Window size 50, stdev variance 6.867136-5.502838=1.364298, mean variance 2.400000
100 shot (mean, stdev) = (291.15, 6.189556208695906)
Window size 10, stdev variance 7.241854-3.326660=3.915194, mean variance 9.000000
Window size 20, stdev variance 6.863327-5.369505=1.493823, mean variance 4.600000
Window size 30, stdev variance 6.662987-5.476806=1.186182, mean variance 2.933333
Window size 40, stdev variance 6.587478-5.858098=0.729381, mean variance 2.475000
Window size 50, stdev variance 6.610320-5.842979=0.767340, mean variance 1.840000
100 shot (mean, stdev) = (285.48, 6.179928409902099)
Full data set is here:
And the python script I used for the calcs I can make public too; it's pretty trivial though.
The upshot is kind of obvious: the larger a window you take, the better the variance in the resulting standard deviation is.
How large a sampling is large enough? It's a matter of scale between the possible error in standard deviation, and how big the trend that you're trying to spot is.
If the possible swing in your results is larger than your trend, it's hard to say your results are conclusive.
in this test we tested over, under, and bore matched, and found nothing of statistical significance in our breakage. sure, our sample sizes were not ideal, but we shot literally all day, out of that gun over 9000 rounds, and what we found was all barrels will break paint.
this pointed us to barrels not really being the cause of barrel breaks.
now, i'd love to shoot until we had something like 20 breaks out of each barrel too, but using those numbers, that would be something on the order of 6 cases from each barrel, and something like 4 days of shooting. sorry, we can't do that.
in this test we looked at insane underbores ... up to .018 or so. we did not start seeing breakage until .012+ so a minor .005" like above just isn't dangerous.
i like that your testing things though, please come by punkworks and post up what you are working on! more data = more better ALWAYS.
Why not? I'll give it a shot.
Blow test with seams engaging the barrel ID. Then downsize .003-.005" (or closest increment down).
But if I get bunkered in the back while swabbing out a messy barrel...
Cockerpunks tests do not account for several important factors that he refuses to acknowledge.
is our testing incomplete? you bet. all testing, of everything is incomplete. thats why we still don't know everything there is to know.
but that doesn't mean its not useful, or we cannot learn to improve performance from it. i've been underboring for 4 or 5 years, as have many many other folks. and as i said, esp on our automags ... the extra efficiency is a godsend.
Last edited by cockerpunk; 08-02-2013 at 05:28 PM.
Your five years of testing, however, has not proven that 20 shots alone is enough. Look at your data, look at my data, look at anyone else's data where you can pick a random run of 20 and compare it against the aggregate longer run. The data strongly shows that if you're looking for differences like what were indicated in that bore test, 20 shots is not enough.
Trying to limit my forum exposure though. I'm actually probably going to start contracting it...
Thanks for all the great info. guys.
I shot 3/4 a case of paint yesterday through the .684 back, (no breaks) and the needle on my air tank barely moved. I used the air from last week! So, I'm pretty sure that the smaller bore increased my air efficiency to a noticeable difference at this point. But, my gut feeling is that the .688 is still slightly more accurate, but slightly less air efficient. Next time I play, I will switch back to the .688 and report back.