Chronograph numbers

[Viper225]

I normally consider in my component costs OR Components on hand when working up loads. The last year this has been an even bigger factor.

If I am working up what I consider to be reasonably accurate numbers I will Fire SIX Rounds that are all loaded alike, and throw out the one shot in that group that is Highest or Lowest and Average the remaining Five Shots.

2560
2563
2559
2571 I would throw this number out of the average
2560
2562

This is Statistically accurate enough for me.

Bob R

[lugerstew]

Viper225: Those are nice chrono numbers!. Which crono do you use?
I use a caldwell and most times I dont feel like it is giving me accurate numbers, I think I have read that most cronos give only + or - 10% accuracy.

[Sarge]

Originally Posted by Sarge

I've had an old BetaMaster for about 15 years. When I first got it, I was obsessed with extreme spread & standard deviation. At the time I had very accurate and powerful loads I'd been using long before I got the Chrony. My first inclination was to tweak those loads for 'better numbers'. Then I came to my senses and decided to not fix what was working.

These days I use it to see what velocity a given load is producing from a specific firearm. Five shots give me that. If the load is producing velocity range established as safe pressures by published reliable manuals and it produces acceptable accuracy, I'm done. I'm not Jonesing for a Nobel Prize for Ballistic Science. I'm just looking to clobber a groundhog, deer or coyote out across the pasture.

Sorry Aguila... I said all that and never answered your question. When I was crunching numbers, I used ten shot strings; mostly because that is what I'd seen done in firearms publications for decades.

[ballardw]

Originally Posted by pgdion

I should add ..... SD is an indication of how likely your data is going to deviate from the average (mean). It's based on typical data fitting a bell curve. Think of how many data points you need to start to shape a bell. It's a lot more than 10. Even 15 is weak. That doesn't mean you need 15 points for good data though. If you have 5 to 10 points and they are all very close, you can be pretty sure the average of those points will give you good results. The SD on that few of points will be pretty meaningless though.

Not quite; standard deviation is a descriptor of spread regardless of the actual distribution shape. With some distributions, Gaussian (or Normal, the "typical" bell curve) it provides a great deal of information (with the mean and standard deviation you can tell what proportion of results will occur within any given range of values). If the actual data is a different shape, such as Uniform distribution (i.e. every outcome occurs with the same probability such a "fair" 6-sided die or flipping an honest coin) not much help.

You typically need a sample "large enough" to tell if a particular example set of data may come from a given distribution. How large depends on the distribution and how certain you need the answer.

[hounddawg]

I suppose I may start sweating chrono numbers when they start having ammo contests, until then I will concentrate on group sizes. I shoot in a lot of matches but never seen one shot over a chronograph and you don't get a mulligan if you put one in the 8 ring

[RC20]

I use a LabRadar Chrono so the following data is accurate. But keep in mind, as long as your Chrono is consistent even if off true, it does not matter if its spot on. If 2750 FPS on the Chrono get you your accurate load, it does not matter if its acualy moving at 2650.

At the base that is true but that does not mean a Chrono does not tell you some relevant information. SD is not it, but a velocity range is.

For instance, I am loading for a hunting 270 (it hates factory ammo). I had the load data, a few rounds left and went to duplicate it.

The 270 did not like my new loads though they were duplicate. Hmmm. Ok, Chrono the old loads and those were 2650 average and the new ones 2600.

I need to up the powder a bit to get back into that velocity range the 270 likes. I may well be at the bottom with the good loads and will explore the upper as well.

[RC20]

An old Finance professor told me that "statistics are like bikinis, what they reveal is interesting, but what they conceal is vital"!

You have the issue of SD relevancy. Its a data piece that goes with FPS, but that does not mean its relevant.

As noted, you can have spot on velocity of 40 FPS spread and you will get a nice low SD.

Yippeee, but the gun does not like the velocity. uhhhhhhh.

The Bikini (SD) by itself is not relevant, its only when it goes with the girl that it is (ES).


Ergo, low SDs reflect low ES. Now SD may have some real world application in statistic someplace, but its nothing more than a reflective number in shooting.

[Unclenick]

As the sample size gets bigger, the ratio of ES to SD grows, as my diagram below shows for a constant SD of one. It grows because all the members of a small sample are more likely to be in the higher probability part of the curve, where a large sample offers more opportunities for data points to appear in the lower probability extremes. You can see it tossing runs with a coin. The majority of tosses tend to alternate heads and tails pretty often. Still, after a while, you accumulate a smaller number that are two heads or two tails in a row, then you get still fewer with three heads or tails in a row, and still fewer with four in a row, and still fewer with five in a row, etc. The longer the run of same-side tosses, the lower the probability of them occurring, but with enough tosses, eventually, they do. It’s the same with shot velocities or shot locations in a group. The values furthest from the mean value are the least probable, but with enough shots, they start to accumulate. Once in a while, one shows up with just a few shots, as may have happened with Viper225’s data.



One thing that is nifty about the root-mean-square basis for calculating standard deviation is the growth with sample size shown in that plot doesn’t change the result of the calculation based on its total data. It remains equal to one. So you don’t usually have to drop out-of-place-looking points from your data. In Viper 225’s data, the difference made to SD by including the higher velocity point he dropped is significant. But unless I knew I had let that round cook too long in the chamber or had got the powder back more solidly over the flash hole before firing or had some other known reason for it to be faster, I’d refire several more sample groups to confirm it was likely an outlier. Dropping data has to be judged carefully because you don’t want to inadvertently bias your result, as often happens when high and low values are tossed out without careful consideration.

Where the standard deviation comes from is it is one of the coefficients in Carl Friedrich Gauss’s equation that plots the bell curve that so neatly describes how nature distributes most things randomly around a mean. The basic equation has three coefficients: one that determines the height of the curve, one that determines the width of the curve, and one that determines the center location of the peak. He knew that for the area under the curve to represent a whole population (100% of it), the area under the curve needed to be equal to one. He then figured out he could replace the height coefficient with a function of the width coefficient such that as the curve got wider, it also got shorter and vice versa in the right proportion to keep the area under the angle always equal to one. That width coefficient is called sigma and is also called the population standard deviation. That’s how you end up with a standard deviation that bounds 68% of the population around the mean. Any sensible person intentionally choosing a bounding point would choose 50% or some other easy-to-use number, but the number that does that is only 0.6745 times as large as the standard deviation, so it doesn’t fit the equation to keep the area under the curve equal to one. Thus, the exact value of standard deviation is really an artifact of the math that is describing nature.

For sample size, you have to choose the certainty you need to determine what constitutes significance. Some examples of choices made by others are:

10. SAAMI’s system of determining pressure and velocity is based on test sample sizes of 10. This is to avoid members having to spend exorbitant amounts of time and money on testing during the manufacturing process. To get away with such a small sample, they make generous allowances for standard deviation and extreme spread. They don’t let an individual round reach the proof load range, but it is allowed to get closer than you might think. This is why you occasionally still get ammunition recalls.

15. Denton Bramwell, who ran a manufacturing process statistics company and who wrote several articles for Varminter Magazine that include the use of statistics, said he is satisfied that he learns enough about a load from a sample size of 15. His article, The Perverse Nature of Standard Deviation, is worth a read.

30. Board member Statshooter, who teaches statistics at the college level, is not satisfied with fewer than 30 rounds in a sample. Thirty is a number that was pretty much the minimum used before Gosset (aka, Student) and Fisher came along, and it is still frequently used today. 30 will let you arrange the data into a histogram that starts to reveal the outline of the bell curve clearly with a normal distribution. It is also the number at which using the sample standard deviation calculation, with its n-1 variance denominator to compensate for small sample size no longer represents much practical improvement in accuracy as compared to using the simpler population standard deviation calculation with n as the mean variance denominator.

100-300. Commercial and military ammunition accuracy testing often involves numbers in this range. One measure of accuracy is to find the smallest circle that still covers 50% of the holes in a 200-round sample. This is called the 50% Circular Error Probable (or circular probable error). You can convert between the two with that factor. Another is to measure and average the vertical and horizontal locations of every hole to find the mean position (the group center), and then take the distance of every hole from that location and find their standard deviation to get the radial standard deviation. If you the radial SD it by 0.6745, it gives you the CEP 50% number.

[hounddawg]

IF ES and SD really make that much difference in group size does it matter what the actual numbers are? If they are really relevant the you should be able to look at a test target and know that group A had the better ES/SD than group B, C, D and E just because the group size was smaller on group A ?

That is why the only time I do velocity FPS now is at the end of my 100 yard development cycle. Three shots with a Magnetospeed just to get the FPS data for my ballistics calculator. Funny thing is my group sizes at long range continue to improve and I get sub .5 MOA performance at long range. For those who want to overcomplicate things feel free to do so, myself I would rather spend my time and effort shooting. It is like a mentor of mine said, there are those who reload to shoot and those who shoot to reload.

[Unclenick]

At 100 yards, the time of flight is too short for gravity to act much on the bullet, so you don't really see much vertical stringing from velocity variation at that short range. This is why Randolf Constantine recommended 300 yards for shooting an Audette ladder. It's short enough that small wind shifts don't take a big toll on POI, but long enough to start to see vertical POI change with velocity pretty clearly. A ballistic calculator will show you that if you had a perfectly rigid gun, 100 fps difference at typical .308W velocities with a 175-grain SMK would only make 0.19 moa of difference to POI at 100 yards. But at 300, it makes 0.66 moa or 2.1" of difference, so you can see the separation round-to round velocity differences make. By the time you get to 1000 yards (by then subsonic), it's a whopping 4 moa and nearly 4 feet of difference. So the effect of ES on POI is mainly a concern for longer ranges.

Another thing SD can alert you to is ignition problems. If you change your primer or your powder lot or start shooting in significantly different temperatures and see a change in SD, it can mean ignition has gotten better or worse. Worse (wider SD, less consistent) ignition is a factor at all ranges because it tends to vary the 3 ms or so delay between the primer being struck and the pressure building enough to start moving the bullet. This means every vibration, muscle twitch, or other problem with keeping the barrel still is acting for different lengths of time, changing where the muzzle is pointed at the moment of bullet exit. This opens groups up.

The bottom line, I think, is that it is so cheap to store data these days that if you can collect data points like your velocity and its SD and ES automatically off your chronograph, there is always a chance it may be useful for future diagnostics, so why not keep it?

[rclark]

At 100 yards, the time of flight is too short for gravity to act much on the bullet

I would add that it depends on 'velocity' (time to target). I wouldn't test my slow revolver cartridges out to 300 yards....

[hounddawg]

I have yet to find a load that groups tight at 100 but fails at 800. Powder charges I only do 3 round groups at 100, seating depth is tweaked at 300 where I do 2 to 7 round groups doing the adjusting at the range. It's my own method that I have developed over the years, works for me. I don't expect anyone else to use or approve it


edit-

On the 2 to 7 rounds. If the first two are a MOA apart the group will not get any smaller with three, four or give. If it can go seven rounds and stay around 1/2 MOA then it is good for twenty if I do my part. Why waste bullets and primers

[RC20]

I reload to shoot.

Maybe Tubbs can shoot good enough to do the data mining and come up with nuances.

The only thing I note (keep) is the Avg, what powder charge got me that average and was it a good group.

I just keep the LabRadar running all the time because its easy and I get an readout on the Average as the COAL is adjusted. But if the ES is wild and its still a good group? Yep I keep that load and see if it will duplicate.

[Unclenick]

It's dependent on barrel timing. The vertical dispersion seen as you step loads up in an Audette Ladder ceases and clusters at spots. Constantine attributed that to harmonic muzzle swing, while Milosovich attributed it to the velocity flat spots in a load string that today folks credit Scott Satterly with figuring out, though he was not yet part of the shooting scene when Milosovich wrote about it. The limitation of the ballistics programs is the one I mentioned in the last post. They assume a perfectly rigid gun. Real guns and riflemen aren't rigid so recoil moments and barrel bending get involved. Nonetheless, the fact even Creighton Audette could not see enough vertical displacement to make his ladder work at 100 yards, but could at 200, with Constantine liking 300 better, proves it is possible to group vertical stringing fairly well at 100 while not having it do well further out. But if your 100-yard load lands in the middle of the flat spot Audette was searching for in the first place, then it won't be an issue.

[stagpanther]

Unless it's a cartridge I never intend to shoot past 100 yds, I never test at that distance if I can help it. I didn't start out that way, but over the years I definitely experienced enough cartridges that grouped well at 100 mysteriously fly apart at 300 yds to push my ladder test distances out. I was never a believer in the "spin stabilization theory," at first, and maybe the greater distance just makes the deviations more obvious for my eyes. I generally don't look just for the magic minimum SD/ES--but the group that is bracketed on either side of the charge weight by very good group/numbers as well that used slightly higher/lower charge weights.

[hounddawg]

When a group falls apart at 300 - 1000 I have found it almost always has more to do with my shooting ability than the load. I also came to the conclusion that when a a slower shot hits higher on the paper than a faster shot it is becasue my POA was a tad higher.

My ego wants to believe I am a machine rest and my aim and technique are perfect shot after shot with god like wind reading ability, my common sense brings me back to reality.

here is a link to a video showing how simply changing the cant of the rifle 1° will change the POI 5 inches at 1000 yards

https://www.youtube.com/watch?v=DJTN82AYcqU

[Unclenick]

Lots to keep track of. No doubt shooting skills end up being the limiting factor when you get everything else right. Per the velocity factor, I've made the mistake a couple of times of letting a round cook in a warm chamber a little too long at 600 yards and getting a 12:00 9 from the extra velocity for my trouble. It's just another of the many variables.

Per my mention of Milosovich and Satterly, is nobody here using the chronograph to generate velocity ladders to look for flat spots?

[stagpanther]

is nobody here using the chronograph to generate velocity ladders to look for flat spots?

That's kinda sorta what I do, I find that adjacent charges (+/- .2 grs or so) that have very close to identical SD/ES will also be very close in velocities. Have you observed the same thing and if so do you think there is a correlation?

[hounddawg]

I used to use the Cortina 100 yard load development for just that Nick but when I started analyzing my development I discovered that my smallest groups almost always had the lowest chrono stats. I just do not feel the need to overcomplicate these days SO all I concentrate on is group height on the powder charge and overall group size when doing seating depth, it does not matter if it is at 100 yards or 800 yards.

The only numbers I sweat these days in load development is the 95% CEP which I want to be below .5 MOA. That way if my POA and wind reading is good I can pretty guarantee a 97% score. For that I use OnTarget software which at $35 is less than 100 bullets

here is a 10 shot practice target that has .4 MOA 95% CEP's, which are in the lower left corner of the box. I over compensated for the wind shifting from 3 o'clock when I did my sighters to 6 o'clock when I shot the group but I was pleased with the overall group size

Like I said earlier it works for me

[Unclenick]

The OnTarget TDS is good software. The ability to virtually overlap multiple targets increases your statistical certainty without making you shoot so many rounds into each group that you can't distinguish the individual holes any longer.

[hounddawg]

well my latest spurge is for a Shot Marker system so my load development may distances my evolve once again. Only thing that bothers me about that is I still do not trust my technique enough to be able to separate the wheat from the chaff. Like I said in a earlier post , my ego wants me to believe I am as accurate as a machine rest BR rig, but the reality is I am human with questionable technique and wind reading skills. I will probably stick with 100/300 for development purposes

The OnTarget TDS is good software. The ability to virtually overlap multiple targets increases your statistical certainty without making you shoot so many rounds into each group that you can't distinguish the individual holes any longer.

This is one of my first F class matches back in fall 2017. It took me until the third match to get my group centered. 189, 190, then a 194 @ 300. This is the composite is of all three targets and sixty rounds. I no longer archive all of my matches since we went to the Kongsberg Target Systems which does not export but I do archive all of my practice targets which my way of keeping a reloading log

[Unclenick]

That's a bummer about the Kongsberg not exporting. Doesn't it log data for the match director at least? I should think they'd want that in the off-chance of a record being set.

I almost pulled the trigger on the Shot Marker, too. Since you've already got one, I am interested to hear how it does. In particular, I am interested in its POI consistency. It says, in a typical frame, you get 2-3mm of possible error. It doesn't say if that is unilateral error or plus and minus error or if it is a fixed offset error or a varying error. If the latter, it's only good to a quarter of an inch at 100 yards, so I would consider it a 200 or 300-yard and beyond device and would still record paper at 100. If it's a fixed offset, then bullets going through the same hole at 100 will still be reported as such, even if the exact point of impact on the paper is off by an eighth of an inch (a big "so-what" situation for load development).

Anyway, I am looking forward to your evaluation and would be interested to learn how closely the tablet target image and the actual target compare.

[hounddawg]

That's a bummer about the Kongsberg not exporting. Doesn't it log data for the match director at least? I should think they'd want that in the off-chance of a record being set.

for the matches we have a second person recording the string, both the shooter and the recorder sign. What some do is take a phone pic of the tablet. No idea how it would work in a record situation

I almost pulled the trigger on the Shot Marker, too. Since you've already got one, I am interested to hear how it does. In particular, I am interested in its POI consistency. It says, in a typical frame, you get 2-3mm of possible error. It doesn't say if that is unilateral error or plus and minus error or if it is a fixed offset error or a varying error. If the latter, it's only good to a quarter of an inch at 100 yards, so I would consider it a 200 or 300-yard and beyond device and would still record paper at 100. If it's a fixed offset, then bullets going through the same hole at 100 will still be reported as such, even if the exact point of impact on the paper is off by an eighth of an inch (a big "so-what" situation for load development).

Anyway, I am looking forward to your evaluation and would be interested to learn how closely the tablet target image and the actual target compare

So far I have only calibrated my targets at 100 yards. I built two frames one for 100 and one for 200 - 1000. I bought a second set of mounts for the short range. I plan on using the load development targets on the small frame. Then bringing the paper back home to scan in for archiving in OnTarget. So far it seem to work fine I will be doing some300 - 500 yard practice with it this coming week.

The primary reason for buying one was for long range practice. Getting real time feed back for POI's for wind shifts, mirage etc. I will be using poster board or back of old targets with stick on dots for various group shooting exercises. F Class John has a lot of really good videos on the Shot Marker you may find interesting.

https://www.youtube.com/c/FClassJohn/videos

[Unclenick]

Thanks. I hadn't seen those.

Yes, the longer-range possibilities as a tool for helping refine wind reading skills is certainly one of the attractions of the system.

[hounddawg]

I figure that if I set up my phone to record me shooting and real time feed back on the POI I can analyze my technique and determine if it was me or the ammo that caused that flyer.