Testing the Testing

[pjifl]

In the end, after trying many things, I used a very fine cut powder. I did not have any spherical but chose one with very short cut grains.

I used both a primer in backwards and also some lead shot of the right size. Or was it an air rifle pellet. The lead was pushed into the primer hole. One problem with any fluid is the possibility of bubbles forming somewhere although a wetting agent helps.

One other advantage of the powder is that it can all be poured out of the case for weighing and nothing gets wet. Of course the result does not correlate with published weights of water.

The biggest problem I had was being uniform in packing the powder and gently trickled it in until it formed a pyramid of repose at the neck. Repeated many times to estimate the precision of the process.

Somewhere I will have data in graphical form looking at the difference in V between some chosen for their large departure from the mean. I will do some searching on old hard drives but no promises.

Peter Smith.

[KHGS]

In the end, after trying many things, I used a very fine cut powder. I did not have any spherical but chose one with very short cut grains.

I used both a primer in backwards and also some lead shot of the right size. Or was it an air rifle pellet. The lead was pushed into the primer hole. One problem with any fluid is the possibility of bubbles forming somewhere although a wetting agent helps.

One other advantage of the powder is that it can all be poured out of the case for weighing and nothing gets wet. Of course the result does not correlate with published weights of water.

The biggest problem I had was being uniform in packing the powder and gently trickled it in until it formed a pyramid of repose at the neck. Repeated many times to estimate the precision of the process.

Somewhere I will have data in graphical form looking at the difference in V between some chosen for their large departure from the mean. I will do some searching on old hard drives but no promises.
Peter Smith.

I use spherical powder as a means of comparison between lots of brass, but not as a means of actual volume batching. Maybe it's me but it is too variable for me to be workable.
I use a machined delrin plug to seal the primer pocket and I use metho for the testing medium.
I have found a rough correlation of weight to volume, but I have to say the indications I have to hand so far indicate that weight batching is not worthwhile with good quality brass, volume batching is far more precise.
My limited testing at this point indicates that whilst using good quality brass batching does not yield any measurable improvement in group size up to 600 metres provided the load is in the middle of an accuracy node.
The quest continues.
Keith H.

[wsftr]

Ok wtf, life's getting bloody boring here too as it's week 4 of lockdown over here but I've had a very close look at the group and personally I reckon your barrel is 1.6" too long.

But don't despair, this video titled "Technobabble" ( of all things ) may help ?

https://www.youtube.com/watch?v=naXLxNX4UZc

Nah mate - not the barrel but close - stock was too rigid - I got something with a bit of flex in it that allowed some PC and she hammered after that.

[ajvanwyk]

The trend line of this plot showed that for each increase in case capacity of 1 gn h2O, velocity drops less than 1 fps ! BTW anyone with QuickLoad could check this conclusion I presume?

So if that is a sound assumption, a volume measurement accuracy of +/- 1gn would be enough to be of benefit - in fact +/- 2gn would satisfy my needs.

Alan,

Had a quick look for you on Quickloads and given a 0.1gn variation in H2O weight the velocity change is plus-minus 1fps.. It's not entirely linear with 0.5gn of H2O variation producing a 7fps variation. Just a small caveat, this is for a RSAUM, shooting 183gn Sierras with AR2209.

Slower powder, like AR2217 seem to have a slightly greater effect with 0.5gn delivering an 11fps variation. The AR2217 load is calibrated to deliver the same velocity as that of the AR2209.

Interesting....

[Gyro]

Looks like an endorsement for 2209 right there ?

[AlanF]

The trend line of this plot showed that for each increase in case capacity of 1 gn h2O, velocity drops less than 1 fps ! BTW anyone with QuickLoad could check this conclusion I presume?

So if that is a sound assumption, a volume measurement accuracy of +/- 1gn would be enough to be of benefit - in fact +/- 2gn would satisfy my needs.

Alan,

Had a quick look for you on Quickloads and given a 0.1gn variation in H2O weight the velocity change is plus-minus 1fps.. It's not entirely linear with 0.5gn of H2O variation producing a 7fps variation. Just a small caveat, this is for a RSAUM, shooting 183gn Sierras with AR2209.

Slower powder, like AR2217 seem to have a slightly greater effect with 0.5gn delivering an 11fps variation. The AR2217 load is calibrated to deliver the same velocity as that of the AR2209.

Interesting....

Thanks Albert. That is an order of magnitude different from my determination, so I need to go back to the ADI data, check my figures and if they look right, then blame ADI?

[ajvanwyk]

[

, then blame ADI?

That's what I do...

[GSells]

Much appreciated thanks Peter. I have sinned and been found guilty of laziness and taking a shortcut haha.

Hey just another wee snippet on Mark F’s shooting through that Queens shoot, 2015. Over the 4 days shooting I remember him firing only two ‘errant’ shots and they were in the same detail at 1000 yards. When he got up he commented that it was perhaps because he “hadn’t set up properly”. When I shoot I just count the good shots amongst all the errant ones !

Now this case capacity business : I would happily bet money ( if I had any ) that VERY few F shooters actually volume check their cases ( and just MAYBE those are the guys that win the big shoots ). I reckon that brass just gets weighed. So if we are to just weigh our cases then we are perhaps ???? not being very thorough. Or are we ? This question has been done to death on other forums as I’m sure most of us know.

What to do ? I would like some tests done and since I’m lazy I need someone else to do them so I can get a free ride off their work. But seriously, a test like this will need some ‘rules’. I seriously reckon some case prep would need to be done first and if one is specifically looking at the capacity/volume then surely we need to fire form the case first ? That’s a no-brainer ? Then we could look at the correlation between the case weight and its volume. Didn't take long to write that but it's gonna take a whole lot longer to do some thorough testing !

I’m hoping just weighing them is “good enough” in the real world, considering all the noise from the countless other dynamics occurring simultaneously. But “hoping for a particular answer” is really not a good place to be in prior to some testing to be sure to be sure. Regards Shortcut Gyro.

Weighing cases is very much a generalisation ! Also depends on how much broad of a ocw tune too . ?? For the record , I weight sort . I'm time poor !

[GSells]

I'm bored so lets throw this out there

here is one - 1000 yrds - shot during a comp. first shoot at 1000 after 100 yrd load dev.
Do ya reckon its case capacity throwing the shots high? what would people do. The group isn't centred as I was testing the load so apart from calling the wind and adjusting the scope no change were made. A lot of F class keep vert under control by clicking.

What to do - was it me, the load, conditions, hold, what?

Conditions or human error . A load like shouldn't just go on the blink unless there was another error in loading ?

[pjifl]

wsftr wrote

here is one - 1000 yrds - shot during a comp. first shoot at 1000 after 100 yrd load dev.
Do ya reckon its case capacity throwing the shots high? what would people do. The group isn't centred as I was testing the load so apart from calling the wind and adjusting the scope no change were made. A lot of F class keep vert under control by clicking.

What to do - was it me, the load, conditions, hold, what?

There is very little that can be deduced from that group. Perhaps a plot of elevation V time will show a trend.

Why not repeat it while measuring V and also recording the wind setting for each shot. You then have something to go on which may preclude certain causes.

BTW, after a few hour's searching I cannot find my work on measuring V from different volume cases. I have not entirely given up. Ironically, the critical plot was actually part of a previous post on this site I did ages ago but I cannot find it in the archives.

Peter Smith.

[ajvanwyk]

wsftr wrote

here is one - 1000 yrds - shot during a comp. first shoot at 1000 after 100 yrd load dev.
Do ya reckon its case capacity throwing the shots high? what would people do. The group isn't centred as I was testing the load so apart from calling the wind and adjusting the scope no change were made. A lot of F class keep vert under control by clicking.

What to do - was it me, the load, conditions, hold, what?

There is very little that can be deduced from that group. Perhaps a plot of elevation V time will show a trend.

Why not repeat it while measuring V and also recording the wind setting for each shot. You then have something to go on which may preclude certain causes.

BTW, after a few hour's searching I cannot find my work on measuring V from different volume cases. I have not entirely given up. Ironically, the critical plot was actually part of a previous post on this site I did ages ago but I cannot find it in the archives.

Peter Smith.

As one example,...

I recorded myself at 1000yd and was shooting on Hexta targets. I recall experiencing loads of verticle and having to adjust quite a bit.... afterwards, I looked at each shot and plotted them on a chart. I then noted every adjustment I made and revised the POI for that shot. By only removing the verticle adjustments I made, I went from a 90.2 to 90.10..... what this told me, and something I now hold very close, is that every rifle has some verticle.... don't over compensate......

Albert

Edit: I guess what I am trying to say, is that we often are the cause of the "bad" group.... but as shooters we love to find excuses....

[pjifl]

Yes - it is always worth reducing the shoot by subtracting all sight changes. Vertical AND horizontal. Wind can influence elevation by AJ. Once all of this is removed the pure rifle/shooter influence is left. And if one also removes any influence from V variations it can be even more revealing.

Peter Smith.

[williada]

Sorry if its more long winded stuff. It may be of interest to some. The following link maybe a good introduction to methods some shooters use. https://www.youtube.com/watch?v=oKxf-dbexMM . It has a link to an Excel program, but beware I could only open it on an older version of Excel. 2019 said it was corrupt.

The author makes the point the concepts are basic and they are, if you have a statistical background. Therefore, the holy grail some extol with low SD's and ES depends on the sample size. In isolation, five shots or even three do not have much confidence associated with them unless they have already come from a tuned rifle. Thirty is a minimum sample size to be statistically significant to determine a guide for tune. It needs to be repeated.

Before I examine the merits of statistical significance in a more advanced way for some that may be interested, there are two huge trade off's shooters have to bear in mind. Firstly, too many shots will ruin a good barrel. It’s probably at its peak around 400 rounds. By the time you break it in properly to get past the velocity hump of conditioning, the window for top draw accuracy becomes narrow. It should not be wasted. The second thing concerns further throat erosion for the period of top draw accuracy. Use time before the hump to condition cases. You should use a reduced load and condition the barrel at the same time then visit formal load development between 100 and 150 rounds IMO.

The initial goal of some shooters is to identify a suitable plateau in velocity by incremental load testing (.2 grains depending on case) with the use of a chronograph using safe loads above and below a pet load, watching for pressure signs on the upper limit. The plateau may contain an OCW pattern, a node or a compensation point or mix of all three.

Chronographs are valuable but, in the past, had a significant error factor. I use Quick load as the go to simulate pressures, barrel time etc. and the chronograph to confirm that. I measure radial spread from 140-yard target having optimized trade-offs with coning, wind and light effects. I only use ladder testing if applicable at very long range because there has been very different terminal flight characteristics in play as confirmed by Jim Boatright which I observed and documented too but could not explain at the time that can alter group shape. Albert may have experienced this at 1000 yards. I do record velocities using a Lab Radar at the muzzle and another Canadian kit at the target for confirmation.

Shooters usually refine charge with seating depth tests or then maybe neck tension to identify tighter groups. I look for stability as a priority, and not necessarily the tightest group. Within the range of seating depths, advanced consideration should be given to where expected erosion may take you. Hopefully a long node may assist and it is not so much an issue. The erosion rate is different between bullets jammed in the lands, just off the lands or well back. It is hard to follow the throat when matches are shot over a few days and in long strings by decreasing seating depth at the venue. That skinny node can tip you out if it’s not taken into account. So, a bit of homework should be done to establish benchmarks for erosion. A trade-off has to be made with the barrel lift process too.

Coming back to statistical significance, there is a big difference between correlation (which shows relationships) and causation. The random, or the outlier maybe discounted as noise etc. in correlation but it will have a cause. It may be a compensation factor, bum shot or a mirage error when sighting in short range load development. A good setup minimizes errors in the process. Much knowledge has been gained in the past from firing from a machine rest with a barreled action that had been properly put together. With many thousands of shots fired, I know if I am in the ball park with charge weight tests with 30 shots, in much the same way pet loads or good loads referred by others because they reflect significant numbers. So, I feel I can use less data to populate my tests, and particularly when the rifle has already been tuned and I am chasing the throat. You know when to stop with experience.

I am in the camp of ES these days for compensation tuning. It’s that so-called random shot or outlier that can lose a match. I mitigate against that to a point using harmonic theory and practice which I am sorry to say is an advanced craft to optimize. There is a third inertia point which I have referred to before long ago in posts, in the atmosphere before the bullet takes free flight which impacts on its exit from the muzzle which a forward of the muzzle tuner can influence. From a statistical point of view, the bell curve used in the video does not always represent a nice neat curve based on the other inertia points i.e. ignition and throat engagement of the projectile. The curve can be skewed left or right or in statistical terms represent kurtosis of high or flat peaks which could have fat tails or long ones. The distribution is distorted. Statisticians can verify by other means. Common tests may include chi square, "F" test and "T" tests if others want to check them out.


There are tests which give statistical validity to ES. Again, I use the actual load development target from 140 yards and do not rely solely on the chronograph but the actual radial measurement of the spread. I think it was a statistician by the name of Grubb using a Monte Carlo simulation with a population of 1000 data points who determined a formula which indicated how much population was required for an error factor reduced to 10%. If this figure is applied as a minimum number of shots to assess ES, it comes out at 7 shots. If several strings of seven are used with incremental load then that error reduces, but you have to shoot quite a few more to be sure. I can live with 10% error with the use of ES as a discriminator.

I don't necessarily rely of linear regression, but do use nonlinear regression to fit curves such as ES data. I have posted in detail about this process before. This post becomes too long to repeat that information and images in Photobucket have gone to God on my old posts.

[Gyro]

Lordy lordy my comprehension rate has lifted. The ES or the SD ? Statistics are useful ( I’m told ) but there’s the “stuff happening on the ground” factor as well.

I gotta 7mm F Open gun that sometimes shoots crazy well. When I first built it I was most sure it was gonna be the be all and end all and even if Rod D was to cross the Tasman I was gonna carve him up. As it happens things haven’t turned out like that. The “skinny node” phenomenon I’m sure is occurring plus all kinds of other stuff’s going on “in there” as williada alludes to. In the freebore and throat area I suspect and I’m not smart enough to sort it out. That’s ok.

Just a brief story about a node prahblem. In 2016 I shot our Nationals at Trentham in FTR. The final is just one 15 shot detail shot at 900 yards on the Saturday but it’s the three days prior to that where all the shooting takes place. Trentham is one of those 4-seasons-in-one-day places. So we started shooting on the Wednesday ( it was a COLD day ) and the gun shot like a dog. Lots of vertical. I was happy with my wind calls but ended up way down the field after day one. Day two was considerably warmer and actually ended up with the sun blazing down and my wife at one point applied sunscreen to my legs while I lay on the mound. The gun shot really well that day. We shot four ranges that day ( 500y, 600y, 900y and 1000y ) and my 200 grain Berger Hybrids went where they were supposed to be going. There were 36 shooters in the field that day, across both FO and FTR and I agged the highest, just for that one hot day. The third day was cold and the gun returned to shooting like a dog again so I limped along …… anyway I tell the story absolutely to not be about ME and what might have been or blah blah blah. The story is about stuff that can and does happen when ya aint smart enough !

Apologies Alan just thought it may help to add some ‘reality’.

This thread started with testing and the reliability of the results. Seems we havn’t even got to 1st base with the case volume/weight question ? And I thought that was going to be an easy one. Just imagine trying to test the case neck tension ‘problem’ ? Good luck with that one ! Attached is some friction discussion.

https://www.motioncontroltips.com/why-i ... -friction/

[Rich4]

Thanks for pointing out that video Williada, I’ve followed them since they started but didn’t watch to many videos just read the articles due to net restrictions, the graphs are the main reason I’m interested in methods of reducing es, to ensure it’s the charge your measuring not inconsistency’s in reloading but I’d been doing it crudely longhand