urbanrifleman
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I guess that guy is saying if you stand back far enough, every plotted line looks like a straight line.
Best if viewed from space.
3 shot group vs ladder tests
- Thread starter JoeInTucson
- Start date
I guess that guy is saying if you stand back far enough, every plotted line looks like a straight line.
Best if viewed from space.
Northridge
Gold $$ Contributor
Working into “3 shot” groups within a broader “ladder” helps document several tendencies General “shape” of grouping how long a tune or tunes will dwell together before migrating. Having three shots is helpful to determine if migration is frequency based or lane change on range… if there is “color “ through out
And ladders has travelled or changed quadrant this is not a lane change or range change… and important to note… helps to determine if barrel heat is at play or barrel compensation is realized as well. As others have stated there is a wealth of knowledge with them a ladder format that doesn’t require mass shots to realize potential…
Shawn Williams
And ladders has travelled or changed quadrant this is not a lane change or range change… and important to note… helps to determine if barrel heat is at play or barrel compensation is realized as well. As others have stated there is a wealth of knowledge with them a ladder format that doesn’t require mass shots to realize potential…
Shawn Williams
This thread has been a very deep and excellent discussion into the velocity ladder and the issues associated with the test data. To those that believe in flat spots one of the things that must be explained is why is energy added to the cartridge not showing up in the velocity. Conservation of energy (AKA the First Law of Thermodynamics) requires that the chemical energy combusted in the round is going to show up somewhere else. It will either be heat loss to the barrel, heat loss to the combustion gasses (ejecta), unburnt powder, or velocity (energy) of the bullet. Further it must be explained as to why these losses or energy suddenly change their relationship for a small increment then change back for another small increment. For the flat spot to be real and repeatable this must be explained by the physics.
Further, in the development of any test, the size of the expected change must be large enough to not be lost in the measurement uncertainty of the measuring equipment and the influence of other factors in the test that effect velocity. In the case of a Radar class chronograph with an accuracy of 0.1% measuring a 2700 fps projectile 95% of all 2700 fps velocities will read between 2697.3 and 2702.7 fps and 5% will fall outside that range. A difference of 5.4 fps. With one sample per charge you have no idea where within that band the particular shot falls relative to its true velocity. Further the very nature of the testing means every component, case, bullet, primer, is different to some extent and the way these differences combine results in variances of velocity that show up in every shot.
Further, in the development of any test, the size of the expected change must be large enough to not be lost in the measurement uncertainty of the measuring equipment and the influence of other factors in the test that effect velocity. In the case of a Radar class chronograph with an accuracy of 0.1% measuring a 2700 fps projectile 95% of all 2700 fps velocities will read between 2697.3 and 2702.7 fps and 5% will fall outside that range. A difference of 5.4 fps. With one sample per charge you have no idea where within that band the particular shot falls relative to its true velocity. Further the very nature of the testing means every component, case, bullet, primer, is different to some extent and the way these differences combine results in variances of velocity that show up in every shot.
jelenko
Gold $$ Contributor
I think it's important to add that, aside from measurement error, there is simply the dispersion of velocities at a given powder charge with all the same components, seating depth, neck tension, etc. We call that the extreme spread.
To determine if there's a flat spot somewhere, we have to shoot enough shots to get a reasonably confident average muzzle velocity. I'm not sure about how many shots are needed to get a 'reasonably confident' muzzle velocity but I know it's more than 1.
That’s the theory - the Satterlee test is mean to be a sensitivity experiment to determine a span of charge weights where slight inconsistencies in charge weight will not influence the POI downrange as much it might at other charge weights.
Using a curve of mine from several years ago, in the green circled region below, I could spill kernels all over between 41.6 and 41.8 and have no velocity consequence, which should yield no vertical consequence on trajectory. Loading in the red circled region, each kernel becomes worth 4fps (slope of the line between those datapoints). So if I load with a +/-0.015grn scale or balance in that circled region, I’d expect +/-4fps as maximum potential influence to velocity, which has a maximum potential vertical influence based on a ballistic solution of 1.6” of extra vertical at 1k - BUT - an RSS estimation of error compounding shows it would likely only present as ~1/8” extra vertical at 1k.
If we loaded with a +/-0.1grn dispenser, the max potential velocity influence due to charge weight variability would be +/-25.5fps, much bigger difference, which running through the ballistic solver would potentially offer a maximum of 10.2” to a 1k group. Again running an RSS for error compounding, the actual vertical would likely be less than 4.1”. A 51fps ES is pretty high, most of us simply aren’t experiencing that.
So that’s the idea - loading in the “node” with a +/-0.1grn dispenser would be safe, 0” vertical influence, whereas the controls would have to be MUCH tighter if loading in the “anti-node”.
**This graph was one of the dataset I was convinced was repeating and repeatable, then 3 years ago, I went through and compiled all of my data from those tests and they overlapped into a straight line which fit inside my standard SD and ES predictions for each respective charge weight.
How many shots are required to achieve confidence in the observation depends upon the variability of the data set and the precision required of the observation.
On Page 2, I shared confidence assessment of your velocity data, even over your 20 shot strings, your average your shotmarker velocity displayed was only accurate within 6-7fps of the true average, with a 95% confidence interval. Granted, I expect the 13-14fps SD’s the Shotmarker picked up would not represent the true SD’s of your MV’s on those strings, but with high variability like that, it takes more shots to establish confidence - for that batch of ammo, it would take more than 20 shots, based on your data provided. So as I described on the previous pages, your data showed ~13-14fps SD, so we’re really only ~34% sure that any velocity on that page is within 13-14fps of its true value (what an average of an infinite population of shots of the same charge would be). That’s not necessarily a problem until we start doing an assessment of flat spots which need the shot to be accurate to within a window of 3-4fps to look like a flat spot instead of higher or lower and look like a ramp.
This is why I’m describing that trying to prove flat spots exist is futile - it WOULD take enough ammo to burn barrels, but all along the way, the data is pointing to the fact flat spots do NOT exist. It’s easier to just accept that and shoot less rounds and promote fruitful loads without worrying about velocity flat spots.
Yes, unfortunately. But there’s already enough push back against the negative assessment done for the validity of the Satterlee/Audette velocity curve, nobody really wants the blowback from doing the same for the Audette POI Ladder. In that discussion, using mean radius from centroid, or normalization data for group size is critical, so we can determine a heat map of where a population of bullets for a given charge would land - represented by 1-3 actual bullets. Guys see that all of the time - a POI ladder puts 3 shots of 3-4 charges within 1/4moa of one another, so then we run with that, and sometimes “loads fall apart” and a guy starting with a couple 2-3” groups at Nat’s ends up finishing with a couple 4-6” groups and blows his agg. Same load, nothing changed, just the Fates delivering statistically probable outcomes in a coincidental order.
This also points towards a differentiation of inductive vs deductive experimentation. Folks think they are doing a deductive experiment, but in the end, shooting small groups at distance is shooting small groups at distance, so no matter what they pick and why, it ends up shooting small because it shoots small. But yes, many folks expect that if we run the same assessment of whether POI ladders work for the reasons folks believe or not, we’ll see the same outcome - but evidence shows that well built rifles shoot small, and shooting a load enough to get to know how it shoots gives shooters enough info to shoot small. Inductive experimental outcomes are still successful, even if they aren’t deductive.
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jelenko
Gold $$ Contributor
Depends on the number of shots. I'm currently using 7-8 shots to get my average muzzle velocity.
Not at all.
But it is real to acknowledge that ONE shot produces a single velocity - and we all know that if we load 2 shots of the same charge, they will NOT produce the same single velocity, let alone if we load 20 or 200 shots of the same charge.
If we simply add our SD above and below to every data point, we realize a few fps of shift for any given data point at each “flat spot” would make the flat spot into a ramp. Let alone if we properly apply standard error bars or the predicted ES… at its core, we’re talking about pulling two heifers out of two herds, squinting to prove one weighs 4 ounces more than the other, and ignoring that the rest of the herd your buying varies by hundreds of pounds between each head.
urbanrifleman
Site $$ Sponsor
Yet, if the dip in the curve repeats, say 10 times or even 100 times it becomes statistically relevant.
Your pre assumption is that any wave in the curve is "in the noise" of a straight line. Of course, one could set out to prove the wave exists byseeing if it repeats. It certainly could.
LVLAaron
Gold $$ Contributor
Agreed. I've never seen someone work so hard to prove something doesn't exist that obviously does.
urbanrifleman
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ballisticdaddy
Silver $$ Contributor
Not to derail this riveting thread but this is the exact reason why I believe we have a hard time getting new shooters into the shooting sports. Does it really matter how one arrives at a load that works for them in their rifle? One member even went so far as to discount a posted score as it was done on the back of tests that he felt were not valid so neither was the actual score that was shot. Sorry but getting tired of reading that there is only one way to do things accurately so I am turning off the computer and going outside to shoot my rifles and enjoy the day without the bickering....hope you all have a great rest of your day as well!
If you have this data to publish, please do, and we all as shooters can learn from the shared evidence.
I don’t even read the long winded one’s. lol!
It’s not a “pre-assumption,” it’s an observation based on a collective body of personal and external evidence which has proven the hypothesis.
Quite to the contrary, ~25yrs ago I was handed a photocopy of a Creighton Audette article which included the velocity curve, which DID establish for me a “pre-assumption” that flat spots existed, and I chased that smoke for over 20 years until I further evaluated whether that “pre-assumption” had any merit and whether it survived the scrutiny of scientific rigor. It didn’t, and it doesn’t. But the alternative hypothesis, that a linear correlation DOES persist, and flat spots are simply caused by the coincidental occurrence of statistically probable results within the inherent noise of the population has been confirmed in every instance I have ever assessed (out of hundreds of evaluations in the last decade). Even the most rudimentary assessment of the data reveals 1) the flat spots do not represent a defensible and confirmed (repeatable) velocity relative to the surrounding velocity points) AND 2) a linear regression fits the overall velocity curve with exceptionally high (.99+) coefficient of determination, meaning even with the inherent error, the linear regression fits extremely well.
Ignoring that data to stick with a pre-assumption that the world is flat - or rather, velocity nodes are flat - is the part which simply doesn’t make sense to me. So I gave up on a belief I had held for over 2 decades.
The defensible argument folks make in this conversation is that the “overlapping impacts” in small roundcount groups aren’t actually telling the story that folks want it to be telling.
That's what Hornady was testing...and yes they got a lot of blowback
As have a lot of other folks. Nobody has actually been able to prove their results incorrect, or produce a defensible body of data which disagrees with any of the results from these multiple houses. The only arguments against these results remain to be the same appeal to authority and post hoc ergo propter hoc fallacies - arguments without defensible evidence. A lot of bark, but we’re all waiting for someone to actually have teeth in their argument to actually bite back.
I agree with you about turning off the computer and going outside, best advice I've heard all day
But in regard to turning off new shooters, as a percentage virtually nobody in the shooting world is even aware of these discussions. Reloaders are small percentage of shooters and the percentage of reloaders who care about it is small. I don't think it's hurting anything to debate it.
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