PDA

View Full Version : Chrono or no chrono??



Salmon-boy
02-29-2008, 09:10 AM
When working up loads with CBs, should one have a chronograph?

Would the answer be different for Rifle or Pistol loads?

pdawg_shooter
02-29-2008, 09:13 AM
I have had a Pact crono for about 8 years now. Used the hell out of it at first, now just used it maybe one or two times a year. Accuracy is way more important to me.

VTDW
02-29-2008, 09:21 AM
Even a cheapie chrono is a must if you push the envelope on velocities IMHO. If you are experienced you can certainly get by just fine without one. Last weekend I had my buddy bring his chrony to the range because I was trying for max velocity with a new boolit powder combo and the loads were compressed. I achieved velocities well over the written load data and the chrony proved it. Was I nervous?...heck yes!! It's a guy thing.:mrgreen: There were no signs of excessive pressure, but still, it was nice to have a chrony there to make sure as it was uncharted waters for me. As usual I found some outstanding accuracy below max load data.

Dave

Bass Ackward
02-29-2008, 09:26 AM
If you are pushing, use a chrono cause you can't develop velocity without building pressure.

If you are going to shoot cast like cast, and use the start low and work up method, it's not a necessity.

Maven
02-29-2008, 09:37 AM
Very nice to have when you're working with some milsurp powders, e.g., IMR 5010, IMR 7383. Also good to have when you're trying to develop a load with a plain-based CB, e.g., the Lee 30-150-TL-PB and wondering why there's lots of leading, but little accuracy.

mike in co
02-29-2008, 10:40 AM
if you are going to do load development, why would you leave a primary tool off the list ?

yes you can "reload" without one, but if you strife to be an "ammo crafter", buy a decent one.

Larry Gibson
02-29-2008, 11:58 AM
I suggest the use of a chronograph always when developing loads. This is especially the case if loads are tested at ranges less than 50 yards. Also if the loads are going to be shot past 50 yards. Accuracy, especially at short range, does not tell you consistancy. A load than is accurate and consistant at short range will also be accurate (given a correct bullet) at longer ranges. I've seen a lot of loads with large extreme spreads of velocity were very accurate at short range but really inaccurate at medium or long range. I suggest the use of a chronograph. Doesn't hurt any thing but it will provide additional information that is useful.

Larry Gibson

HABCAN
02-29-2008, 12:05 PM
Larry, I have a question for you. (I have a PACT.) I know we all try for minimal readings of SD and ES, but I would appreciate your opinion on what is 'too much'.

beagle
02-29-2008, 12:16 PM
If you're shooting "stock" loads out of a reloading manual and stay within the parameters with listed bullets you probably won't need one.

If you do any shooting that uses components outside the loads listed in manuals, you definitely need one. There is very little data listed for H & G, Saeco, RCBS, Lee and some of the later Lyman bullets. Very little data listed for milsurp powders and no pressure readings. Almost no seating depths. All of these things affect the velocity...and pressure of a load.

A chrony won't give you pressure readings but it will tell you velocities which are directly tied to pressure. I fear that many of us get away with murder using cast bullets as they're much more forgiving pressurewise than the jacketed variety.

Get a chrony, use it and use your head and record your results meticulously. You'll be miles ahead if you do./beagle

Larry Gibson
02-29-2008, 12:52 PM
Larry, I have a question for you. (I have a PACT.) I know we all try for minimal readings of SD and ES, but I would appreciate your opinion on what is 'too much'.

When deveoping loads (5 shot groups) for rifles I look for an ES less than 30 fps with a SD of 30-40% of the ES.

To confirm a load I will shoot 2-5 10 shot strings or two 20 shot strings looking for an ES of 50 fps or less with the attendant SD of 3-40% of the ES. Most often my confirmed loads have an ES less than 25 FPS over a 10 shot string.

Since I shoot at longer ranges I pay more attention to the ES and then look to see if the SD falls in the correct range. Many only quote the SD with thier loads but I've seen some pretty small SDs with large ESs. To quote Dr. Ken Oehler; "you should consider standard deviation; don't worship standard deviation."

Larry Gibson

218bee
02-29-2008, 05:30 PM
As a reloading nut I feel it is a must have. I do not load to maximum to see where velocity/pressure spike each other but as a hunter and long range shooter knowing the velocity in "MY GUN" is information I want instead of guessing what velocity I am at.

xtimberman
02-29-2008, 07:07 PM
I felt like I had operated successfully without a chronograph for decades, and now I can't imagine how I did it!

Seriously, a chrono saves me a whole lot of time when working up loads - particularly when developing loads for auto pistols that function within a narrow power range. I usually like to target a specific velocity range first, then tweak COAL, charge weight, etc. to fine-tune accuracy and function. With a good library of load data and a chronograph, I can often find the desired velocity quickly without wasting too much time and too many bullets.

A chronograph removes a lot of the guessing when working on the safe maximum end of a load combination. You can quit long before you get to the cratered primers and head separations.

xtm

runfiverun
02-29-2008, 10:52 PM
sooner or later the chrono is going to come out!

just because the "book says" don't make it so.

standles
02-29-2008, 10:57 PM
I find my chrono invaluable in my tinkering with loads for cast and the Jword.

I don't kow how I ever got along without one.

Steven

joeb33050
03-01-2008, 08:48 AM
When deveoping loads (5 shot groups) for rifles I look for an ES less than 30 fps with a SD of 30-40% of the ES.

To confirm a load I will shoot 2-5 10 shot strings or two 20 shot strings looking for an ES of 50 fps or less with the attendant SD of 3-40% of the ES. Most often my confirmed loads have an ES less than 25 FPS over a 10 shot string.

Since I shoot at longer ranges I pay more attention to the ES and then look to see if the SD falls in the correct range. Many only quote the SD with thier loads but I've seen some pretty small SDs with large ESs. To quote Dr. Ken Oehler; "you should consider standard deviation; don't worship standard deviation."

Larry Gibson

We need a lot of MVs measured with a chronograph, probably 30 or more, to know much about the true MV and SD.
ES or extreme spread is mathematically linked to Sd or standard deviation. If you know one, you can calculate the other. SD is a "better" measure of variation.
While the chronograph is handy with near-max loads, and with unknown or surplus powder, and while many claim that the chronograph is crucial for load development, I have NEVER found a shooter who could or would explain how the chronograph helps in accurate load development with known powders. NEVER. And I've asked.
See the CBA nationals results, see the majority of ESTIMATED MVs.
joe b.

Whitespider
03-01-2008, 10:03 AM
My vote goes for the chronograph. Virtually every shot fired off my bench is over sky screens. But my shootin' range is in my back yard, makes it easy for me.

felix
03-01-2008, 10:19 AM
Chronos are fun! But, only after the load is developed. The only ES I measure is the spread at the target. The velocity ES would be much more important for when the target is GOING to be beyond the point of normal interest. ... felix

Larry Gibson
03-01-2008, 12:16 PM
We need a lot of MVs measured with a chronograph, probably 30 or more, to know much about the true MV and SD.
ES or extreme spread is mathematically linked to Sd or standard deviation. If you know one, you can calculate the other. SD is a "better" measure of variation.
While the chronograph is handy with near-max loads, and with unknown or surplus powder, and while many claim that the chronograph is crucial for load development, I have NEVER found a shooter who could or would explain how the chronograph helps in accurate load development with known powders. NEVER. And I've asked.
See the CBA nationals results, see the majority of ESTIMATED MVs.
joe b.

You never asked me.

The answer is simple; with the chronograph you know the consistancy of the load which holes in paper do not show nor tell you. Granted repeated shooting of a load will tell you if it is consistant (what some the bench resters do) but with the chronograph you know with one test. I have shot some pretty good groups at shorter ranges with some pretty inconsistant loads (ES's well over 200 fps). At longer ranges the inaccuracies of such loads is readily apparent. With the chronograph such loads are eliminated in the development stage with no further effort or waste of componants spent on them. You also know the MV and can then accurately calculate the trajectory and sight adjustments without guessing or time/resource consuming tests. For hunting the chronograph tells you if your loads are within the parameters you want for proper terminal effects. I've seen 200-300 fps +/- difference between chronographed velocities and published velocities including cast bullet velocities. The use of the chronograph has cut my load development time down considerable as I get excellent loads quickly without having to experiment with many so-so loads in between.

Also while SD is a measure of uniformity for a long range shooter ES is more important. You don't know what the velocity of each round is as you must go with the Average. SD only tells you that a certain percentage (the larger the number of rounds tested the greater the %) of the shots in the test will fall within the SD +/_ of the average "mean" velocity. With a 10 shot string this means that 7-8 of the shots fall within the SD fps of the mean velocity. What about the other two shots? (they are outside the SD fps figure) With a 3 or 5 shot test the SD is even less meaningful. With the shorter shot strings the ES and SD are certainly good indicators and can be used to judge whether a load has merit for further development but a small SD with a 3-5 shot group is pretty much meaningless if taken by itself. I've seen numerous loads with small SDs but a larger than expected ES as one round was a considerable fps apart from the others. With such a load that round will go out the bottom (if a much lower velocity) or out the top (if a much higher velocity). This means a miss or crippled game if hunting or loss of points if in a match. It may very well just be frustrating if plinking. The problem with such a load is you never know when that odd round is in the chamber. I'd rather have a consistant load which is why I look for the smaller ES and the comparative SD percentage wise. As Dr. Oehler mentions, I don't worship SD. BTW; I've been chronographing loads since '75 so my experience with them is extensive.

Larry Gibson

jhalcott
03-01-2008, 02:00 PM
Yes, a chrono is needed to be certain of the velocities you are getting. It will also tell you when you are getting the most from your powder charge. When you get LESS increase in FPS from a standard increase in charge weight, you know you are at or near the upper limits of that load. I normally work up to an accurate load THEN use the chrono. I may tweek the load at that point.

S.R.Custom
03-01-2008, 03:08 PM
... Accuracy is way more important to me.

Same here. I've got a fair amount of gear, but never bought a chrono. I've always worked up loads for accuracy and paid strict attention to pressure signs. In that context, the velocity is what it is... There's enough published load data out there with velocity figures that you can compare your loads to to it and get a fair idea of what's going on. The exact number has never been that important to me.

That said, the only time I've used a chrono was when I was building my 7mm Mag long range rifle with the 30" barrel. I was dying to know how fast those 175 gr slugs were coming out of that long of a pipe (3035 fps). And even then, it was just a matter of curiosity. The SD (11) merely repeated what I already knew from punching the paper.

snuffy
03-01-2008, 03:35 PM
I seldom set up to test loads without the pact chrono set up also. If I figure I don't have time to mess with it, I don't go shooting at all.

It's a different story if I'm just going to do some fun shooting, plinking with established loads.

joeb33050
03-03-2008, 09:09 AM
The chronograph calculates the average velocity of the sample of bullet velocities measured.
Bullet velocities vary, and two measures of this variation are commonly calculated by the chronograph. These measures are "extreme spread" or ES, and "standard deviation" or SD. (Statisticians call ES the "range".)
So, for example, we might shoot a sample of 10 bullets over a chronograph, and see that the average velocity was 1506 feet per second (fps), the ES was 62.4 fps, and the SD was 20 fps.
SD has the characteristic that its value is independent of sample size. If we shoot sets of 4 shots with a given load, or sets of 24 shots with that same load, the SD will average the same. Velocity SD, for any given load and set of conditions, is a constant.
ES for that same given load and set of conditions varies with sample size, the number of shots fired and chronographed. ES is mathematically connected to SD so that if the sample size and ES are known, SD is easily calculated.
With 10 shots fired, ES is 3.08 times SD; keeping in mind that SD is a constant. So in the example above with SD of 20 fps, ES should be 3.08 times 20 fps or 62.4 fps; vs. the example 62.4 fps. (For 10 shots, SD times 3.08 will AVERAGE about the ES, individual samples will vary in the relationship.)
The relationship works the other way, of course. For 10 chronographed shots and ES of 62 fps, SD = ES/3.08 or 62/3.08 ~3.08.
Here's a table of the sample size/corrections from SD to ES and back:

2/1.13 Sample size of 2, SD times 1.13 = ES, ES/1.13 = SD
3/1.69
4/2.06
5/2.33
6/2.54
7/2.79
8/2.85
9/2.97
10/3.08
15/3.47
20/3.73
30/4.08
40/4.32
50/4.50
75/4.80
100/5.03

When we talk about the SD and ES of velocity of a given load, we're talking about the same variation with numbers that are a multiplier/divider apart. They're the same thing, as long as the sample size is the same.
If the example was changed to reduce the sample size to 5, knowing that the SD will remain constant at 20 fps, we would expect the ES to be 20 X 2.33 = 46.6 fps. The ES falls from 62.4 fps to 46.6 fps. ES varies with sample size, so it clearly doesn't make any sense to talk about ES without specifying sample size. ES without sample size is meaningless, SD is constant and independent of sample size.
If we chronograph 6 shots with Remington 2 1/2 primers and 15 shots with WLR primers-everything else the same- we might get an average velocity with both loads around 1400 fps; ES with the 6 shots of 76.2 fps and ES with the 15 shots of 104.1 fps. Do the WLR primers cause more velocity variation than the Remington 2 1/2s? No, because if we divide 76.2 by the 6 shot multiplier/divider of 2.54 we get SD = 30 fps; and if we divide 104.2 by the 3.47 we also get SD of 30 fps. We didn't see a change in variation, we saw a change is sample size.
Remember, these relationships hold on the AVERAGE, over lots of samples. Your individual results will vary, but the principles hold true.


joe b.

Larry Gibson
03-03-2008, 01:44 PM
The SD remains constant (% wise) only if the samples ingnition is uniform. If all 5 shots of the small sample have uniform ignition the SD will be different from one where 1 or two shots (same load) have poor ignition. Also numerous samples (lets say 5 five shot strings of the same load) more than likely will have slightly different average velocities along with slightly different SDs. The SD is an important measurement of uniformity but remember that a SD 14 fps only means that 2/3s of the shots will be within 14 fps of the average (mean) velocity. Question then arrises; what about the other 1/3 of the shots that are outside of the 14 fps SD? This is why we must also consider the ES when evaluating loads. Especially those used at longer ranges.

To Quote Dr. Oehler; "When ever you use standard deviation, remember there is an important corollary of Murphy's Law. Its regular use can replace many mathematical theorems and complicated statistical procedures.

Large groups usually repeat.
Large groups with large standard deviations always repeat.
Small groups caused by luck never repeat.

And so I've found, especially with cast bullets.

Larry Gibson

cbrick
03-03-2008, 02:14 PM
Larry Gibson's post mirror's my experience fairly closely. I too have been chronographing since the 70's and have kept detailed notes on all load devolpment. Notes include details from powder lot numbers, temperature and humidity, date, groups, alloy, BHN and more. A prime value of the chrono AND the notes is in comparison of your loads in your guns. What did this change do in this gun? What does this powder do at that temperature. Does a BHN change effect groups or velocity? Primer change effects and much, much more. The more load comparisons you can make the higher the value of all of the notes and all of the previous testing. It builds on itself and becomes more and more useful and pertinent to your loads in your guns.

In the early 90's I put all my notes in the computer and used the computer exclusively ever since. Live and learn I guess, after a couple of moves and not giving much thought to the paper notes of the past I no longer had them. One hard drive crash and I no longer had any notes from about 20 years of testing. Notes today are kept on two computers AND a paper notebook.

Another prime benefit of the chrono in working up loads is a pressure indication. NO, the chrono will not tell you what the pressure is BUT in mid powder capacity cartridges (mostly what I work with, say 7 TCU up through 308 Win) an increase of 0.5 gr powder will net right at 50 fps velocity gain. It may be 40 fps or 65 fps but it will be right around 50 fps. The first 0.5 gr charge increase that does NOT net an increase of the average 50 fps and you have reached the pressure max for that cartridge, powder, bullet combination. From that point on the only thing that can be gained is more pressure with NO velocity gains and very possibly, even probably velocity and accuracy loss. Its the point I back off a half grain.

Rick

TexasJeff
03-03-2008, 08:52 PM
if you are going to do load development, why would you leave a primary tool off the list ?

yes you can "reload" without one, but if you strife to be an "ammo crafter", buy a decent one.

I'll second this.

I used to chrono my reloads when shooting IPSC to see where I was on the "major/minor" power scale. It was the chronograph that told me my +p+ LE-issue 124 grain Hydrashoks were giving me almost .357 Magnum velocity out of the gun I was carrying at the time. I felt better about carrying a 9mm after that, because with a .357 Magnum, I fear neither man nor beast.

But it was during my initial years in reloading that I really enjoyed the chronograph. Enjoyed seeing what the powder people guestimated for fps versus what my guns and loads actually shot. Each gun and each barrell shoot different. I like knowing what's going on.

'Course, my chronograph went belly-up some years back and I haven't replaced it . . . yet.

Jeff

James C. Snodgrass
03-03-2008, 09:27 PM
If livin' in the dark is what a man is after by all means avoid it. But IMHO I doubt that any one on this site can't afford a chrono, I know that most of us have spent more on one mold.[smilie=1:

Whitespider
03-04-2008, 07:09 AM
.........SD is easily calculated.
With 10 shots fired, ES is 3.08 times SD; keeping in mind that SD is a constant. So in the example above with SD of 20 fps, ES should be 3.08 times 20 fps or 62.4 fps; vs. the example 62.4 fps. (For 10 shots, SD times 3.08 will AVERAGE about the ES, individual samples will vary in the relationship.)
The relationship works the other way, of course. For 10 chronographed shots and ES of 62 fps, SD = ES/3.08 or 62/3.08 ~3.08.


joe,
That just ain’t so, SD calculation uses a complicated formula.
Standard deviation is the ”root mean square deviation of values from their arithmetic mean”. To find the SD of just 2 values requires six arithmetic calculations. None of those calculations use the ES of the values.

1- find the arithmetic mean of the values
2- find the deviation of each number from the mean
3- square each of the deviations
4- sum the obtained squares
5- divide the sum by the number of values
6- take the non-negative square root of the quotient =SD

Microsoft Excel has a Standard Deviation function, =STDEV(cell range) and I used it to calculate SD for two strings of 10 numbers each, both with an ES of 100. Using your formula (ES/3.08), 100/3.08= SD 32.46, but in neither case did that work out to be true.

example 1
100
150
150
150
150
150
150
150
150
200
ES=100 - SD=23.57

example 2
100
100
100
100
150
150
200
200
200
200
ES=100 - SD=47.14

SD is not constant and has very little to do with ES. SD is a mathematical formula that gives “probability” (or best guess) of result based on a sample. I’m with Larry on this one, SD is all but meaningless without knowing the actual ES of the sample load.

joe - What your formula(s) does (basically) is take the Highest Possible and Lowest Possible SDs for a given sample range value and average the two. That defeats what SD is all about.

joeb33050
03-04-2008, 08:30 AM
joe,
That just ain’t so, SD calculation uses a complicated formula.
Standard deviation is the ”root mean square deviation of values from their arithmetic mean”. To find the SD of just 2 values requires six arithmetic calculations. None of those calculations use the ES of the values.


SD is not constant and has very little to do with ES. SD is a mathematical formula that gives “probability” (or best guess) of result based on a sample. I’m with Larry on this one, SD is all but meaningless without knowing the actual ES of the sample load.

joe - What your formula(s) does (basically) is take the Highest Possible and Lowest Possible SDs for a given sample range value and average the two. That defeats what SD is all about.

Whitespider;
This ain't a stat class, but I'll try to help you out here.
The SD of velocities for any given load/gun combination is what it is, a constant, until maybe the gun barrel wears. Here we're talking about the population or process SD. This area gets sort of involved and opinionated.
Means if we measured a lot of velocities we'd get a mean and SD describing the population.
Now, sample SDs calculated from samples of size "N", will vary. So, if we shoot sets of say 5 shots and calculate the SDs, those SDs will vary. Say we shoot a lot of sets of 5 and chronograph them and calculate the SDs. The SDs will cluster around and average the population SD. There is no difference between the AVERAGE sample SD and the population SD. NOTE--The sample SD is an UNBIASED ESTIMATOR of the population SD.
Now, using the velocities for the same sets of 5 shots, calculate the ES, called by those statisticians the "RANGE". The ES values will cluster around a mean or average, but that mean WON'T be the population SD. it will be 2.33 times the population SD. So, we say that for sample size of 5, the ES = 2.33 times the POPULATION SD, or through the magic of algebra, that the POPULATION SD equals ES/2.33. For N = 5. ES is a BIASED estimator of SD, with N =5 the bias is 2.33.
Sample ES and SD are estimators of POPULATION SD. For any given sample these two estimators may not give the same estimate of POPULATION SD, but over the average of many samples they will.
Remember, if we shoot and chronograph 15, for example, shots, and calculate the sample SD and ES, unbias the ES estimator of POP SD, and see that they are different-we don't know which is closer to the POP SD.

The ES has been used as an estimator of SD for many years, particularly in Statistical Quality Control where it made statistics possible on the shop floor before the computer.
A computer search on range and SD will provide a wealth of information.
Also see "Tables of Range and Studentized Range", H. Leon Harter, "The Annals Of Mathematical Statistics", December 1960.

It's interesting to see your "root mean square" definition of SD, I use that definition or approach and seldom see others use it. The AC voltage in the wall is a RMS value, as is the measure of surface finish made with a profilometer, RMS microinches.

So, I hope this helps you out. I'd be happy to send you the 1960 article with tables that I find very helpful.
Good luck;
joe b.

joeb33050
03-04-2008, 08:43 AM
The SD remains constant (% wise) only if the samples ingnition is uniform. If all 5 shots of the small sample have uniform ignition the SD will be different from one where 1 or two shots (same load) have poor ignition. Also numerous samples (lets say 5 five shot strings of the same load) more than likely will have slightly different average velocities along with slightly different SDs. The SD is an important measurement of uniformity but remember that a SD 14 fps only means that 2/3s of the shots will be within 14 fps of the average (mean) velocity. Question then arrises; what about the other 1/3 of the shots that are outside of the 14 fps SD? This is why we must also consider the ES when evaluating loads. Especially those used at longer ranges.

To Quote Dr. Oehler; "When ever you use standard deviation, remember there is an important corollary of Murphy's Law. Its regular use can replace many mathematical theorems and complicated statistical procedures.

Large groups usually repeat.
Large groups with large standard deviations always repeat.
Small groups caused by luck never repeat.

And so I've found, especially with cast bullets.

Larry Gibson

Larry;
You're confusing the SD of a SAMPLE-which is what you and all of us see calculated on the chronograph, and the SD of the POPULATION. Sample SD and unbiased sample ES are both estimators of population SD. We can only ESTIMATE population SD, can't measure it.
ES is ALWAYS greater than Sample SD.
Velocity distributions with all components held as constant as possible- means same powder, charge, bullet, lube etc-same everything within the bounds of the possible, as we should experiment-will be A distribution with A SD, SD is constant for the POPULATION.
I think you need to unconfuse the population and sample and their SDs.
Remember, ES with varying Ns is a measure of N, not velocity spread.



joe b.

brshooter
03-04-2008, 09:01 AM
I'm on my 3rd. Chronograph. I use the same techique as cbrick, and it works well. As to records, I keep detailed records with targets. Hot loads worked up in early morning temps sometimes turn into mightmares at mid afternoon. Helps you find that the rifle has a sweet spot at what velocity to give you consistant small groups.

Larry Gibson
03-04-2008, 12:29 PM
Joe

I'm not confusing anything. SD is not a constant. Perhaps you should further research that. SD is derived from from the 6 calculations that Whitespider discusses. As you see from his example the SD can be very different from the sets of figures with the same ES.

You are correct that what we get is a "sample". However the larger the sample the more relevent it is to the "population". The only way to know the exact ES, SD and mean velocity of a "population" is to shoot the entire population. Not really a practical thing to do. However getting a good "sample" gives you a reasonable expectation (or educated guess) of how the "population" will perform.

For example; I get a good ES with attendant SD of 30-45% of the ES from a 5 shot string of a test load. I load up 3 ten shot strings or 1 twenty shot string or 5 five shot test strings to test. All are good "samples". When fired if these test strings also demonstrate the same good ES and SD as the original 5 shot string then we have a good indication that the "population" will also perform as well. The ES and SD are not expected to be exactly the same but are expected to fall within the expected parameters of a "good load". I can then expect that additional rounds of this exact load using the same componants (the rest of the "population") and shooting them out of the same firearm will give close to the same ES and SD of the "samples" tested. In other words I can expect the rest of the rounds loaded to fall within the ES and be close to the average (mean) velocity. Yes that is an "estimation" but in my opinion it is then a pretty educated one.

If we take Whitespiders two examples I would bet the load with the SD of 47 would shoot a more consistant group than the example with the SD of 23. The 23 SD group would no doubt have 6-7 shots in a smaller group than the 47 SD group. It would also have 3-4 shots that were "flyers"; definately shots out of the group. The size of the groups may be the same but the 47 SD group would be consistantly more accurate to shoot. The reason is if we zero the 47 SD to the center of the group and the 23 SD to the center of the 6-7 shot group (where the SD tells us it is "good") we will find with the 47 SD group no shot is more than 1/2 the group size away from the point of aim. Conversly with the 23 SD group the 6-7 shots are no more than 1/4 of the way from the point of aim but the 3-4 "flyer" shots will be 3/4+ the distance from point of aim.

Fact is you will shoot worse with the load with the smaller SD in this case. That is why the two, ES and SD, must be considered together and the % relation of the SD to the ES must be correct.

Larry Gibson

felix
03-04-2008, 02:57 PM
You have to take the distance of each shot about the center of the target (POA), and then correlate that with the muzzle velocity ES of those same shots, and then repeat the same at a different yardage. Now correlate the whole shootin' match as a composite to get any real meaning of the math. Besides, because we are talking vectors here, it would make good sense to use a cubic function for deviants rather than using a quadradic function. Numerical signs and angles are significant for this logic, and must be taken into account. All of this would measure the capability of the system to place shots consistently. Hint: Taylor series solves many complex arrangements fairly easily. We're getting out of the realm of a hobby. ... felix

joeb33050
03-05-2008, 06:45 AM
Joe

I'm not confusing anything. SD is not a constant. Perhaps you should further research that. SD is derived from from the 6 calculations that Whitespider discusses. As you see from his example the SD can be very different from the sets of figures with the same ES.

You are correct that what we get is a "sample". However the larger the sample the more relevent it is to the "population". The only way to know the exact ES, SD and mean velocity of a "population" is to shoot the entire population. Not really a practical thing to do. However getting a good "sample" gives you a reasonable expectation (or educated guess) of how the "population" will perform.

For example; I get a good ES with attendant SD of 30-45% of the ES from a 5 shot string of a test load. I load up 3 ten shot strings or 1 twenty shot string or 5 five shot test strings to test. All are good "samples". When fired if these test strings also demonstrate the same good ES and SD as the original 5 shot string then we have a good indication that the "population" will also perform as well. The ES and SD are not expected to be exactly the same but are expected to fall within the expected parameters of a "good load". I can then expect that additional rounds of this exact load using the same componants (the rest of the "population") and shooting them out of the same firearm will give close to the same ES and SD of the "samples" tested. In other words I can expect the rest of the rounds loaded to fall within the ES and be close to the average (mean) velocity. Yes that is an "estimation" but in my opinion it is then a pretty educated one.

If we take Whitespiders two examples I would bet the load with the SD of 47 would shoot a more consistant group than the example with the SD of 23. The 23 SD group would no doubt have 6-7 shots in a smaller group than the 47 SD group. It would also have 3-4 shots that were "flyers"; definately shots out of the group. The size of the groups may be the same but the 47 SD group would be consistantly more accurate to shoot. The reason is if we zero the 47 SD to the center of the group and the 23 SD to the center of the 6-7 shot group (where the SD tells us it is "good") we will find with the 47 SD group no shot is more than 1/2 the group size away from the point of aim. Conversly with the 23 SD group the 6-7 shots are no more than 1/4 of the way from the point of aim but the 3-4 "flyer" shots will be 3/4+ the distance from point of aim.

Fact is you will shoot worse with the load with the smaller SD in this case. That is why the two, ES and SD, must be considered together and the % relation of the SD to the ES must be correct.

Larry Gibson

As I said, this isn't a stat class. You can believe and do whatever you wish, opinion triumphs over fact, as usual.
joe b.

Whitespider
03-05-2008, 09:18 AM
As I said, this isn't a stat class. You can believe and do whatever you wish, opinion triumphs over fact, as usual.
joe b.

Joe,

FACT; Standard Deviation is the “root mean square deviation of values from their arithmetic mean”.

FACT; Six arithmetic calculations are used to find Standard Deviation.

FACT; Standard Deviation is most accurate when the “arithmetic mean” is equal to the “arithmetic median” of the sample (a condition known as “normal distribution”).

FACT; Samples (and populations) of firearms ammunition with HIGH ESs typically have “arithmetic mean” and “arithmetic median” some distance apart from each other (rendering the SD less accurate).

FACT; I did some research Joe; your formula is not intended to calculate actual SDs or ESs. Your table of corrections is used to ESTIMATE Standard Deviation when only the “Sample Size” and “Extreme Spread” are known (actual values of individual samples are unknown), AND the distribution is assumed to be “normal” (mean and median equal or relatively close).

FACT; I’ve checked your formula against a bunch of my records; IT JUST AIN’T SO! Ammunition rarely has “normal distribution”, if it did we wouldn’t need a chronograph to do anything except show us velocity.

If your formula was correct for determining population SD with ammunition, the larger samples should be closer to your formula. In fact, the larger my recorded samples, the farther away the recorded SDs are from your formula.

S.B.
03-05-2008, 10:11 AM
Yes, I use my Pact on every session for working up loads for both rifles and pistols. Either that or your just guessing what velocity your getting?

felix
03-05-2008, 10:14 AM
Again, Joe, statistics is only an ATTEMPT to explain the FACTs of realism! Because statistics is a man-made set of rules, you can exactly define these rules to be FACT! These facts are those being discussed by Whitespider and they are NOT the facts of the natural system we live by. So, please, don't insinuate opinions are on the same plane as facts; statistical calculations are nothing but a collection of opinions about facts. There is no way any kind of opinion can overtake fact. ... felix

Larry Gibson
03-05-2008, 01:06 PM
Joe

I did not derive the mathematical equations to calculate SD nor did I make the definition of SD. SD is a standard set of equations that are accepted as fact by far more learned men than you or I. Those equations are also the standard fact with which the arms/ammuntion industry, chronographs and computors (also those who wish to do the tedious long hand) determine SDs. Unless we use the accepted standard, or fact if you will, we will be comparing apples to oranges if we use a different method of calculation. That is fact, not my opinion.

Larry Gibson

HORNET
03-05-2008, 08:32 PM
IIRC, back when I took a statistics class the book claimed that the sample standard deviation was an estimate of the population standard deviation but it had been determined that the sample SD converged with the population SD if the sample size was 30 points or more. FWIW, in SPC I always used a minimum sample size of 30 pieces for the initial number crunching and used +/- 4 standard deviations to estimate the E.S. for products.

joeb33050
03-06-2008, 12:06 PM
Whitespider;
Maybe this is a stat class. I'll try to help you guys out.

"FACT; Standard Deviation is the “root mean square deviation of values from their arithmetic mean”."
The population SD = RMS deviation, true. However, the SD is also some other things. Normaldistributions have inflection points at the SDs, and there are are a lot of SDs.There's 1 SD above the mean, 2 SDs above the mean, 4 Sds below the mean, etc. At each there's an inflection point, where the second derivitive goes to zero.
The SD, along with the (arithmetic) mean are the defining variables in the definition of (formula for) the normal distribution.

"FACT; Six arithmetic calculations are used to find Standard Deviation."
Well, not true, not a fact. RMS deviation = population SD, but I can't imagine how or when we might try to calculate a population SD. A FACT is that SAMPLE RMS deviation isn't, I don't think, a good estimator of POPULATION SD. Give it a try, against EXCEL calculations or your own. Now why is that…….?(A prize if you can tell me!)

"FACT; Standard Deviation is most accurate when the “arithmetic mean” is equal to the “arithmetic median” of the sample (a condition known as “normal distribution”)."
I don't know what "most accurate" means. You're confused here, again. The median is another "mean" or "average" or indicator of central tendency. The median value of a set of data or a population is that value which there are as many values above as below. In the set 1,2,3,4,5; 3 is the median-there are two values, 1 and 2, below it, and two values, 4 and 5 above it. (There's also the mode, the most frequntly occurring value. And many others.) Now your logical error. All normal distributions have the median = the arithmetic mean or what we call the "average"; but not all distributions with arithmetic mean = median are normal. Consider the distribution of age of 70 year old men. Their average and median age is 70 years, but the distribution of age is not normal. No, it isn't. How about the age of first graders?


"FACT; Samples (and populations) of firearms ammunition with HIGH ESs typically have “arithmetic mean” and “arithmetic median” some distance apart from each other (rendering the SD less accurate).

I don't know that this is so. I think that you're saying that gun velocities aren't distributed normal. If you have some data, I'd like to see it.
Again, "SD less accurate", what does it mean.
We assume that many variables are distributed normal, so that analysis can be done. Many times we don't KNOW that the variable is distributed normal. I would suspect that gun velocities ARE distributed normal, don't know.
This would be interesting to look at. How about sending that data?

"FACT; I did some research Joe; your formula is not intended to calculate actual SDs or ESs. Your table of corrections is used to ESTIMATE Standard Deviation when only the “Sample Size” and “Extreme Spread” are known (actual values of individual samples are unknown), AND the distribution is assumed to be “normal” (mean and median equal or relatively close).+

I don't have a formula. I attempted to tell Larry that ES and SD are related, and that ES is a function of both SD and N, the sample size. The-not my-table of corrections is or may be used to estimate SD from ES when N and ES are known. We can also know the values of the sample variables. Whether or not we know the values of the sample measurements, we can still estimate SD from the combination of ES and N. Again, we assume a normal distribution.

"FACT; I’ve checked your formula against a bunch of my records; IT JUST AIN’T SO! Ammunition rarely has “normal distribution”, if it did we wouldn’t need a chronograph to do anything except show us velocity."

Formula? Please send or post data showing that velocity isn't distributed normal.


"If your formula was correct for determining population SD with ammunition, the larger samples should be closer to your formula. In fact, the larger my recorded samples, the farther away the recorded SDs are from your formula."

See above.
I'll go through some chronograph data and post the results here.

Joe b.

joeb33050
03-06-2008, 12:40 PM
Again, Joe, statistics is only an ATTEMPT to explain the FACTs of realism! Because statistics is a man-made set of rules, you can exactly define these rules to be FACT! These facts are those being discussed by Whitespider and they are NOT the facts of the natural system we live by. So, please, don't insinuate opinions are on the same plane as facts; statistical calculations are nothing but a collection of opinions about facts. There is no way any kind of opinion can overtake fact. ... felix

OK Felix, you're next;
Statistics isn't "an attempt", it isn't a "man-made set of rules", statistical calculations ere not "nothing but a collection of opinions about facts". Statistics isn't an opinion.
Statistics is a branch of mathematics, a mathematical topic, a mathematics division, a part of the greater "mathematics".
I told my students that defining statistics or any subject of study such as, for example, geology or religion or sociology, is hard to do in a few words. But, I told them that a short definition of statistics that I like is "a part of mathematics that translates numerical information into statements in words". So, statistics allows us to make statements such as:"Based on a sample of 456 persons polled, we find that 57% of citizens prefer chunky peanut butter to smooth peanut butter. We're 95% sure that the 57% is within +/- 3%, means we're 95% sure that 54% to 60% of the citizens.........."

Now, there is a fact that the ES and SD of a set of data is related, that SD is a function of ES and N, and it is a fact that there are folks offering opinions about statistics and this relationship. As you know, Felix, it is improper to offer opinions about facts. Opinions don't have any place in discussions of the value of pi or e or the atomic weight of zirconium.

The facts of realism? Felix, what can that mean? If you have something to say, how about short declarative sentences? Otherwise, I begin to wonder...........
joe b.

joeb33050
03-06-2008, 12:54 PM
[QUOTE=HORNET;300846]IIRC, back when I took a statistics class the book claimed that the sample standard deviation was an estimate of the population standard deviation but it had been determined that the sample SD converged with the population SD if the sample size was 30 points or more. FWIW, in SPC I always used a minimum sample size of 30 pieces for the initial number crunching and used +/- 4 standard deviations to estimate the E.S. for products.


I agree
I like N=/> 30, in SPC it was often difficult to get a sample of 30. In chronographing it is difficult to measure 30 velocities from the same distribution. With N=30, ES ~ 4 SD-see the table above.

For more on this go to the book at http://sports.groups.yahoo.com/group/CB-BOOK/, in FILES.
See 6.6 HOW TO WORK UP AN ACCURATE RIFLE LOAD;
under that see CHRONOGRAPHS AND LOAD DEVELOPMENT
then CHRONOGRAPHS AND STATISTICS
(Three things that Dr. Oehler never told us)
joe b.

joeb33050
03-06-2008, 12:59 PM
You have to take the distance of each shot about the center of the target (POA), and then correlate that with the muzzle velocity ES of those same shots, and then repeat the same at a different yardage. Now correlate the whole shootin' match as a composite to get any real meaning of the math. Besides, because we are talking vectors here, it would make good sense to use a cubic function for deviants rather than using a quadradic function. Numerical signs and angles are significant for this logic, and must be taken into account. All of this would measure the capability of the system to place shots consistently. Hint: Taylor series solves many complex arrangements fairly easily. We're getting out of the realm of a hobby. ... felix

How about telling us what this means, Felix?. Remember, velocity is a vector quantity. More explanation is needed, I can't understand what you wrote.
joe b.

joeb33050
03-06-2008, 01:10 PM
Joe

I did not derive the mathematical equations to calculate SD nor did I make the definition of SD. SD is a standard set of equations that are accepted as fact by far more learned men than you or I. Those equations are also the standard fact with which the arms/ammuntion industry, chronographs and computors (also those who wish to do the tedious long hand) determine SDs. Unless we use the accepted standard, or fact if you will, we will be comparing apples to oranges if we use a different method of calculation. That is fact, not my opinion.

Larry Gibson

Larry;
Let me try to help.
I can think of several ways to estimate population SD, none of which is "wrong". Calculate sample SD, calculate ES and correct, graph the sample and find the inflection points, graph or calculate areas under the curve. There are, for many variables, different ways to estimate values. Temperature is molecular velocity. We can measure it by looking at the height of a column of mercury, the voltage in a thermocouple, the amount of bend in a bi-metallic strip or the points at which some crayon-looking marks melt. All ways to estimate temperature, all different.
Don't get hung up on this, it's easy. SD is a function of ES and N. ES is a function of SD and N. You must take N into account when talking about variation, even in bullet velocities.
joe b.

joeb33050
03-06-2008, 02:08 PM
There are 13 chronograph results on the POWDER POSITION SENSITIVITY Excel workbook that's been under ERRATA on the book site for about a week. It's still there.
Calculate ES (call it w on the spreadsheet/workbook).
Correct for Ns to get values of SD
Compare the ES values of SD with the Excel values of SD
EXCEL SD/ES SD = average of 93.7%, on average EXCEL SD was 93.7% of ES SD.
This varied across the 13 samples from 82.1% to 106.1%. N averaged 13, went from 7 to 17.
The sample sizes are small.
The EXCEL SDs are estimates.

I think ES is doing a fine job of estimating SD.

If you want the workbook-original-go to the book site and look under ERRATA.
If you want the updated workbook, just ask and I'll e-mail it.

joe b.

Larry Gibson
03-06-2008, 02:16 PM
Joe

All that discertation to whitespider and felix not withstanding, the fact remains that SD is not a constant which is the point of disagreement. SD varies from sample to sample because the componat parts of the sample vary from sample to sample. In simpler words if we compare two samples with the same ES; the individual velocities of a given sample will differ from the individual velocities of the next sample. Hence the SD will be different between the two samples as two different sets of velocities are used. That is a statistical fact.

Larry Gibson

joeb33050
03-06-2008, 02:59 PM
Joe

All that discertation to whitespider and felix not withstanding, the fact remains that SD is not a constant which is the point of disagreement. SD varies from sample to sample because the componat parts of the sample vary from sample to sample. In simpler words if we compare two samples with the same ES; the individual velocities of a given sample will differ from the individual velocities of the next sample. Hence the SD will be different between the two samples as two different sets of velocities are used. That is a statistical fact.

Larry Gibson

You're still confusing SAMPLE and POPULATION SD and mean.
For any given constant gun/load combination, the mean and SD of the POPULATION of velocities, when properly measured, are constant. There's one distribution of velocities, that distribution is completely defined by the/it's mean and SD
The mean and SD of samples varies. And we know how these vary. Not news.
ES corrected is a fairly good estimator of SD, POPULATION SD. See above for DATA!!
POPULATION mean and SD of velocities are constant, as long as the testing method is correct.
Constant, and that is the statistical fact in question.
joe b.

Larry Gibson
03-07-2008, 12:58 AM
You're still confusing SAMPLE and POPULATION SD and mean.
For any given constant gun/load combination, the mean and SD of the POPULATION of velocities, when properly measured, are constant. There's one distribution of velocities, that distribution is completely defined by the/it's mean and SD
The mean and SD of samples varies. And we know how these vary. Not news.
ES corrected is a fairly good estimator of SD, POPULATION SD. See above for DATA!!
POPULATION mean and SD of velocities are constant, as long as the testing method is correct.
Constant, and that is the statistical fact in question.
joe b.


Joe

That is a good "red herring" but you are still confused. SDs quoted when using chronographs are SDs of the sample, not the estimated SDs of the population. SDs of the sample are not constant. That is what you said and it ain't so, no matter how much techno equations or postulations you throw out. You now agree with this because you say so now in your last post; "The mean and SD of samples varies." So if you agree that the SD "varies" what is your point?

Larry Gibson

joeb33050
03-07-2008, 08:42 AM
Joe

That is a good "red herring" but you are still confused. SDs quoted when using chronographs are SDs of the sample, not the estimated SDs of the population. SDs of the sample are not constant. That is what you said and it ain't so, no matter how much techno equations or postulations you throw out. You now agree with this because you say so now in your last post; "The mean and SD of samples varies." So if you agree that the SD "varies" what is your point?

Larry Gibson

Larry;
We're getting close here, I hope that this is worth it. This must be wicked boring for most readers.
Chronographed SDs are SDs of the samples. Absolutely true!!!
But
Chronographed SDs ARE estimates of the population SD
Sample SDs are not constant, they vary. Absolutely true!!!
But
The population SD is constant-(as long as testing is done correctly/reasonably)

We sample to learn about populations. We want to know what velocity we can expect from a gun/load combination in the future. We sample velocities. Those sample velocity sets have means, SDs, ESs and other values.

Unfortunately, we frequently stop here.

We could and should use these means and SDs/ESs to estimate the population mean and SD,
so that we can make statements, in words, about what we know.

For gun velocities, there are two and only two (that I can think of and that seem helpful) statements that can be made:
1. With this gun/load combination, we are 95% sure that mean velocity is 1555 fps, +/- 57 fps.

2. With this gun/load combination, we are 95% sure that the SD of velocity is 46 fps, +/- 7 fps.

We can be more than 95% sure, but then the 57 fps goes up. The 57 fps and the 95% are inversely related, we can solve for any value of % or +/-, but the other goes up or down.

Now, we don't do this analysis, but whether we do or not, the facts are in the sample numbers. I covered a lot of the analysis in the book, it ain't hard and that's the truth.

You may not make these statements, but when you chronograph a load the statements exist, disguised in the N, Average, SD and mean of the velocities.

joe b.














.

Larry Gibson
03-07-2008, 02:12 PM
Joe

Looks like we're on the same page of the hymn book, finally! Always good discussing things and sorting them out with you.

Larry Gibson

Whitespider
03-07-2008, 11:53 PM
This is almost unbelievable Joe, the defense of your position is bordering on the ridiculous. First of all, we’re talking about firearms ammunition, a 20-round sample may easily represent 20, 25 or even 50% of the “relevant” population. Let’s say BrandX produces a lot of 100gr .257 ammo totaling 60,000 rounds, to the manufacturer the total population equals 60,000. But Bob the deer hunter buys four boxes on sale at WallyWorld, enough to last him 4 or 5 years. By the time Bob needs more ammo that lot# will be gone, so the total relevant population for Bob is 80 rounds. Bob uses one box (20 rounds) to sight in his rifle and chronographs them at the same time, that’s 25% of the population. Bob can be pretty much assured that the sample chrono results will mirror the population when fired in HIS rifle. Now let’s say the following are the results of his chrono session. - In fact this is ACTUAL DATA from a load I was working up in my 20” .257 Roberts. (I’ve rounded the sample velocities, removing the tenths)
(2904,2899,2613,2606,2890,2905,2894,2910,2901,2587 ,2904,2899,2879,2912,2884,2572,2909,2892,2887,2908 )
ES=340 / SD=125.3 / MEAN=2837.8 / MEDIAN=2896.5 - The MEAN and MEDIAN are some distance apart, this is NOT normal distribution. If I use your “table of correction” SD=340/3.73 or 91.2, that’s a long ways from 125.3, but let’s use 91.2. I should expect 34% to fall between 2747-2838 (actual is 0%), 16% above 2919 (actual is 0%), 34% between 2838-2919 (actual is 80%), and 16% below 2747 (actual is 20%), notice the highest recorded velocity (2912) is below 2919. If we use the SD of 125.3 I should expect 34% between 2753-2838 (still 0%), 16% above 2963 (still 0%), 34% between 2838-2963 (still 80%), and 16% below 2753 (still 20%) and the highest recorded velocity is well below 2963. I could shoot 50 more or 500 more, or the whole population and the ES/SD/MEAN/MEDIAN are not gonna’ change much because this load had ignition problems (a primer change fixed it, we’ll get to that data soon). Standard Deviation is not close to being correct BECAUSE the MEAN and MEDIAN are some distance apart, the data does NOT have NORMAL DISTRIBUTION! Simple fact is, the SD is incorrect and irrelevant, a comparison of ES/MEAN/MEDIAN is what we should be looking at. What we should be looking at is the Skewness factor, I don’t remember how it’s calculated, just use the Skew function in Excel (I keep my records in Excel). In this case the Skew is -1.16, negative means the data is skewed to the lower side of the MEAN. Whenever Skew is higher than 0.8 or lower than -0.8 the SD becomes virtually unusable as an indicator of load performance. There’s also a Kurtosis value I could throw in here, but for now I’ll keep that one to myself.

Ok, I changed to different primer (I’m not gonna’ list each velocity, you’ll have to trust me), fired twenty and got this for data.
ES=23 / SD=7.2 / MEAN=2953.1 / MEDIAN=2952 / SKEW=0.3 / LOW=2943 / HIGH=2966
Your Table of Correction SD=6.2, that’s pretty darn close to the 7.2 but no cigar. I was so tickled with the results I fired ten more to see if the data would hold. Here are the results for all thirty rounds.
ES= 25 / SD=7.3 / MEAN=2953.6 / MEDIAN=2953 / SKEW=0.1 / LOW=2941 / HIGH=2966
Your Table of Correction SD=6.1. I’ve added more data, putting my sample closer to the population, yet the two SDs are moving farther apart. By adding ten rounds my ES and SD did get slightly higher (your SD lower), yet the SKEW has moved closer to “0”, I’m totally confident that my numbers aren’t going to change more than one or two, maybe three percent over the population. Remember, we’re talking reloaded ammo here, I doubt the total population would ever be much over 150-200 rounds because by then I’d have another lot of powder, or primers, or bullets, or whatever.

One more example, this time from a 32 Magnum revolver. I recorded the data at 20 rounds and then again at 50 to see how the performance would hold or change.
20 rounds; your Table of Correction SD=11.5
ES=43 / SD=12.6 / MEAN=1107.4 / MEDIAN=1111.5 / SKEW=-0.7 / LOW=1081 / HIGH=1124
50 rounds; your Table of Correction SD=10.4
ES=47 / SD=12.9 / MEAN=1106.2 / MEDIAN=1108.5 / SKEW=-0.6 / LOW=1079 / HIGH=1126
Again, as more data is added the difference between actual SD and your estimated SD gets larger.

Really, because of the SKEW factor, Standard Deviation should have never been included with chronograph data. A much better and informative piece of data is “Mean Absolute Deviation” as it doesn’t need distribution to remain accurate, it uses absolute numbers. Thankfully, one of my chronos, an old Pact Model 1, calculates MAD instead of SD. That’s the unit I grab when it’s time to start getting serious.

Whitespider
03-08-2008, 09:15 AM
joeb,
I’m not really trying to say that the “Table of Correction” doesn’t or won’t work, but it leaves the “total population” as an open ended value. And that’s fine if we’re talking about ALL the ammo in LotX, fired in ALL the guns chambered for that cartridge and fired under ALL possible conditions.

But I’m not interested in “ALL”, the only data of use to me is the data relevant to “my” total population, fired in my gun, under the conditions I’ll be using it.

:drinks:

joeb33050
03-08-2008, 09:36 AM
Whitespider;
Let's see if I can help you with this.
Population size, in the world of the statistician, is thought of as infinite. Assumed to be infinite. We might want to know the height of 8-year-old girls in the USA. We take a sample, measure them, do some calculation and come up with a mean and SD. We describe the population with this mean and SD. Is the population "the 8 year old girls in the US"? No. The population is "the infinite number of 8 year old girls having identical lives to the sample and the girls currently in the US"
Sample velocities describe a population of an infinite number of velocities shot with same gun and load.
If we don't consider the population infinite, we have to consider any number, no matter how large, as a sample.
We're getting into the weeds here, lots of talk and argument about this with grad students.

Now to your first set of 20 velocities. I put them on an EXCEL spreadsheet and sorted them. The bottom four are 2572 to 2613. The top 16 are 2879 to 2912. What you have here is a bi-modal distribution, or more properly in this case, samples drawn from two different populations. (Think of a sample of 8-year-old girls drawn from both the USA and a very poor nation. We might see two modes, with the poor nation girls height being less than that of the USA girls.)
As soon as we see that two populations are represented in the sample, we STOP. In SPC this is considered a process which is OUT OF CONTROL, we stop doing statistics and search for the problem.
There is nothing to be done with statistics with this data that will help describe A population, because we've got TWO populations from which we're sampling.
(Put your data up, sort it, calculate the mean and SD for the 4 then the 16, find ES, correct, and see how closely the corrected Less match the calculated Sods.)
Let me say this as clearly as I can. If the sample data shows two distributions, all statistics stops because it is meaningless from here out. At least for purposes of this discussion.

"OK, I changed to a different primer……" Here you're seeing how sample values change, here as sample size increases. If you want to see another example of mean and SD changing with real world chronograph results, go to the book and the chapter/section cited, and watch them change. Remember, the population is infinite.

Now for your 32 magnum data, same response as above. You're seeing sample values change. Keep in mind that the calculated SD from the chronograph is from sample data, we don't know what the pop SD is.

This all started with the FACT the chronographed velocities have calculated SDs that come from a sample and are estimates of pop SD, and that ES is from a sample, can be corrected to an estimate of pop SD. That sample SD is a function of pop SD, ES is a function of pop SD AND N.

I hope that this helps you out; today's chronographs give us extremely precise information but don't tell us how to use that information or what it means.
If you have any specific question I'll try to answer it; if you're really interested I suggest a course in Statistics.
Joe b.

Whitespider
03-08-2008, 02:26 PM
We’re a lot closer on this than you might think joe. I’ll even concede that all you say is true in the world of statisticians.


...Population size, in the world of the statistician, is thought of as infinite...
...watch them change. Remember, the population is infinite...
...today's chronographs give us extremely precise information but don't tell us how to use that information or what it means.
Joe b.
This is where the differences in thinking begin. In the world of Bob deer hunter, everything is finite. If Bob chronos 20 rounds of his lot of 80, and a statistician wants to call that a sample of a sample, so be it. But in Bob’s world, 20 is a sample of the finite population. For Bob’s purposes, the 20 round sample is going to give him a much better idea of the performance of his remaining 60 rounds than any number corrected to an infinite population. This is why I said SD should’ve never been included in chrono data. You’re right, most owners of chronographs have no real idea what the figures are telling them. But, when analyzing the chrono data a shooter must keep in mind the size of his finite population (or total sample to you), and most ammunition populations (what a stat guy would call the total sample size, I guess?) are much smaller than most would think.


This all started with the FACT the chronographed velocities have calculated SDs that come from a sample and are estimates of pop SD, and that ES is from a sample, can be corrected to an estimate of pop SD. That sample SD is a function of pop SD, ES is a function of pop SD AND N.
Joe b.
Well, for me it started with....

...if the sample size and ES are known, SD is easily calculated...
...Here's a table of the sample size/corrections from SD to ES and back:...
joe b.
...because I instinctively knew that any stats corrected to the infinite population would be less accurate for (and less useful to) Bob the deer hunter and his finite population (sample). Read again the above.


...if you're really interested I suggest a course in Statistics.
Joe b.
Been there...done that...I’m a realist. I understand the concept, but basing anything on the infinite just ain’t where I live. Think about it, if the pop. is infinite a shooter has no idea what percentage of the total his sample represents, try explaining that to Bob the deer hunter. Another reason I believe that SD should be left out of chronograph data, or at least a lot less attention paid to it.

Oh yea, my apologies to Bob (whoever he is), I didn’t mean to infer that he’s too dense to understand.

joeb33050
03-14-2008, 09:02 AM
Here's what I've extracted from the responses above.
Chronograph uses

When developing loads with milsurp powders
When developing loads outside published load data, = different bullet, powder, etc.than in published data.

The assumption here is that pressure is related to velocity; that knowing velocity enables the shooter to broadly estimate pressure and stay safe.

To calculate L.R. drop and approximate sight settings
To check measured V vs. published V
To see/if V change as components change; bullet BHN, OAL, primers, etc
To check V vs. temperature
To find the V sweet spot
To calculate the IPSC power factor

Larry Gibson (and some LRBP shooters) have said that short range accuracy + consistency (ES or SD) = L.R. accuracy, and that SR accuracy without consistency = (sometimes) no L.R. accuracy. This means that some loads, accurate at short range, with high ES or SD, are inaccurate at long range; and that it is more likely that loads accurate at short range, with low ES or SD, will be accurate at long range.
I have seen only one instance where a load, accurate at 100 yards, was inaccurate at 200 yards. But, I don't do and haven't done enough long range shooting to know about this. The chronograph allows us to see the ES and SD of the loads.


Some contend that efficiency, the change in V per incremental change in grains of powder, falls off about upper limit, and pressure rises sharply. Example of the notion: Increasing the powder charge by a grain yields a V change of 50 fps for a while, then a grain increase yields less and less increase in V. Where the V increase per incremental change in powder charge falls off, rapid pressure increases are coming. The chronograph allows us to see the changes in V.


My question, obviously not asked clearly, is this. Is there some way that the chronograph can be used to find an accurate load outside from the uses above? With a reasonable powder, primer, bullet etc combination, how does the chronograph help me find the accurate load?

joe b.

Maven
03-14-2008, 12:32 PM
It seems to me that there have been several articles in the "Fouling Shot" and "Handloader" lately which mentioned accuracy, e.g., Charles E. Petty's "The Effect of Brass on .223 Accuracy" in "Handloader #252" and pretty much anything by Mike Venturino in the same magazine on long range BP accuracy. While those articles show chrono. data, none even suggests that its use leads to more accurate results. E.g, Petty's Table II, "Accuracy Test Results" (p. 73) shows accuracy in inches by brand of brass he used, but also velocity, ES and SD. Not surprisingly, there's not a 1:1 relationship between ES & SD and accuracy, but I'll be damned if I know or can figure out just what that relationship is. What seems to matter more, again not surprisingly, if you think about it, is case neck concentricity: less runout usually means greater accuracy.

What's the role of the chrono. in all this? I'm not sure, and maybe am stating the obvious, but it allows you to refine a given combination of powder, primer, CB, OAL, brass (concentricity more than headstamp) so as to produce repeatable results with respect to velocity, ES and SD. I.e., it's a tool which allows you to fine tune a load, not one that magically causes accurate results.

Cherokee
03-14-2008, 12:53 PM
OK......I find a chronograph helpful in eveluating both rifle and handgun loads, but I got along fine for 20 years without one.

oso
03-14-2008, 01:31 PM
Chuck, I have fun getting an idea of bullet velocities 10-12' from the muzzle for my loads out of my rifles and hand guns and shotguns. I like making graphs of average velocity vs powder charge for various bullets in my cartridges of choice. I use the info to find out when I want to back off.
I also record target results but seem to get more correlation with results of chamber casts and tailoring bullet fit. Haven't figured out how to graph that.
Infinity divided what I know is not significant but keeps me fed.

cbrick
03-14-2008, 01:47 PM
Maven fairly well summed up my use of the chrono. It’s a tool to be used to make decisions from as in another thread on the use of alloy BHN testers. The BHN tester cannot tell you what the alloy is and a chrono cannot pick out the most accurate load but they both give a good amount of very useful information.

Not often but I have seen loads that gave consistent better accuracy with worse chrono numbers than other loads. The only way to know this for certain is shooting many groups with both. I have seen loads that were very accurate at 150 meters with great chrono numbers and wouldn't hit a target at 200 meters. Probably a velocity/twist problem but the chrono can't tell you that.

For me working up loads without a chrono would be much like driving around out in the country on a moonless night with no headlights, yep, I might get there but uh . . . Why not use the headlights? The chrono is a tool that can help guide us in the right direction just as another very valuable tool . . . Shooting groups. Not a magician, just a tool.



Here is an excerpt from Dr. Ken Oehler on Standard Deviation.

The secret of making smaller groups is uniformity. Other things being equal, the more uniform you can make the ammunition, the more likely it will shoot to the same hole. Uniform velocities are simply another indicator of uniform ammunition. Uniform velocities do not guarantee small groups, nor do large variations guarantee large groups. There are no guarantees but you can put the odds on your side. When velocities are uniform, you can assume you have a proper primer for the powder, that you have a reasonable powder for the case and the bullet, that you did a good job of measuring the powder and that your cases were of uniform capacity. Uniform velocities tell you very little about bullet quality, the bedding of the action and barrel or if the gun vibrations induced by the firing just happen to fall in a sweet spot. When erratic velocities and small groups predominate, your bedding is probably good and you have a good average velocity for that powder/bullet combination, but be suspicious of your primer choice and firing pin. When you experience both erratic velocities and large groups, go ahead and make significant changes in bullet, powder or gun; you probably aren’t close to any perfect combination.

Theoretically, you could use the standard deviation as the only measure of the uniformity of the ammo. The common limitation on the formal use of standard deviation and other statistical procedures in shooting is the number of shots required. Statisticians call it sample size. Invariably, statisticians want to see at least 20 shot samples. Nobody questions that firing more shots into a group will give a better statistical measure of the accuracy and the standard deviation but it’s expensive and time consuming.

Quite bluntly, trying to measure the velocity uniformity of your ammo by chrono-graphing only five shots is in the same league as determining it’s accuracy with a single 5 shot group. A solitary 5 shot group is an indicator, but you can’t guarantee it will repeat itself. Likewise, a standard deviation number should be considered only as an indication of uniformity. Although standard deviation is the best available measure of velocity uniformity, it is still not good enough to be considered the overall measure of ammo uniformity. Use the standard deviation numbers as indicators of uniformity but use them along with other indicators of a loads performance.

Large groups usually repeat.
Large groups with large standard deviation always repeat.
Small groups caused by luck never repeat.

Lloyd Smale
03-14-2008, 04:42 PM
you guys is comfusin me. I turns mine on and shoots a slug throw it looks at the numbrs it reads. I then uses this number to impres all my friends (thats a ly as i doent have any freinds)

Larry Gibson
03-15-2008, 12:56 AM
Larry Gibson (and some LRBP shooters) have said that short range accuracy + consistency (ES or SD) = L.R. accuracy, and that SR accuracy without consistency = (sometimes) no L.R. accuracy. This means that some loads, accurate at short range, with high ES or SD, are inaccurate at long range; and that it is more likely that loads accurate at short range, with low ES or SD, will be accurate at long range.

joe b.

Joe b.

Your conclusion on what I think is absolutely wrong. I have seen many, many loads that were accurate AND consistant at short range that wouldn't shoot for sh*t at long range. I've seen many, many loads that shoot wonderful at 50 yards but loose it some whare between there and 100 yards and shoot improved cylinder at 100 yards. That is why I consider testing at 100 yards to be the minimum distance for testing loads for a cast bullet rifle. I find when testing loads at 100 yards if a load groups well (that is accurately) has a low ES with an SD 25-40% of the ES it probably will be accurate at longer ranges. The decision that the load is accurate should be based on a minimum of; average velocity, ES, SD and groups should be a 20 shot string, two 10 shot strings or 4 five shot strings.

Then if developing a long range load it is ALWAYS best to test at the longest range practical, preferably at the longest range it is to be shot. Many 1 moa loads do not hold up at 500 yards or 1,000 yards. Conversly; a load that will hold the 10 and X ring at 1,000 yards will certainly shoot well at 100 yards. Also for a cast bullet hunting load; if the load is accurate at 200 yards it will be accurate at 50 or 100 yards.

That is what Larry thinks as it is straight from the horses mouth.

Larry Gibson

joeb33050
03-15-2008, 07:17 AM
Joe b.

Your conclusion on what I think is absolutely wrong. I have seen many, many loads that were accurate AND consistant at short range that wouldn't shoot for sh*t at long range. I've seen many, many loads that shoot wonderful at 50 yards but loose it some whare between there and 100 yards and shoot improved cylinder at 100 yards. That is why I consider testing at 100 yards to be the minimum distance for testing loads for a cast bullet rifle. I find when testing loads at 100 yards if a load groups well (that is accurately) has a low ES with an SD 25-40% of the ES it probably will be accurate at longer ranges. The decision that the load is accurate should be based on a minimum of; average velocity, ES, SD and groups should be a 20 shot string, two 10 shot strings or 4 five shot strings.

Then if developing a long range load it is ALWAYS best to test at the longest range practical, preferably at the longest range it is to be shot. Many 1 moa loads do not hold up at 500 yards or 1,000 yards. Conversly; a load that will hold the 10 and X ring at 1,000 yards will certainly shoot well at 100 yards. Also for a cast bullet hunting load; if the load is accurate at 200 yards it will be accurate at 50 or 100 yards.

That is what Larry thinks as it is straight from the horses mouth.

Larry Gibson

Larry,
Here's the point I'm interested in that I think you make.
If we start testing at 100 yards; accurate consistent loads are better L.R. candidates than accurate inconsistent loads.
The LR big bore guys tell about the more accurate higher ES load (at 100 yards) being LESS accurate at L.R. than the less accurate lower ES load (at 100 yards).
This is the part of what you've said that's I'm interested in here; if I've got it right.
joe b.

joeb33050
03-15-2008, 07:37 AM
What's the role of the chrono. in all this? I'm not sure, and maybe am stating the obvious, but it allows you to refine a given combination of powder, primer, CB, OAL, brass (concentricity more than headstamp) so as to produce repeatable results with respect to velocity, ES and SD. I.e., it's a tool which allows you to fine tune a load, not one that magically causes accurate results.

Maven;
This is what I can't understand. What do you do and how do you do it? Here I sit with a pretty accurate rifle and a load that has been selected from the available candidates. Bullet, diameter, BHN, powder, charge, primer and brass. It shoots OK, but not as well as I'd like. I've done the chamber cast and primer pocket uniforming and case neck annealing trimming turning and all that stuff. I can change any element, any component. How do I use the chronograph in finding a more accurate load? What does the chronograph tell me, that I need to know, that a 100 yard set of targets don't tell me.
I've been asking this, probably not clearly, for some 5 years now.
joe b.

Bass Ackward
03-15-2008, 08:00 AM
My experience for longer range is that a load can be accurate and group well at 100 can have poor ES. But when you step on out, the wider the ES, the earlier stringing will become noticeable. Fairly common sense since we know different velocities have different trajectories. So your "grouping" may still remain MOA, but be ruined vertically by trajectory. Understanding the difference has been my key to diagnosis and proper corrective action.

But the load / gun combination will still determine how stable that bullet is launched and how long any design takes to go to sleep. This really affects BC and therefore velocity regardless of twist rate. So measuring ES at the muzzle doesn't reflect ES down range. Which is why some guys can shoot wide meplats to longer ranges than other people. FME

Whitespider
03-15-2008, 08:38 AM
With a reasonable powder, primer, bullet etc combination, how does the chronograph help me find the accurate load?
joe b.

Hmmmmm...... For me, that would depend on the purpose of the load and the gun it would be fired in. I mean, I would use the chronograph differently when developing a load for a long range varmint load than if I was working on a cast boolit load for my -06. I could write a “War And Peace” size volume on the different ways I use the chrono to “find” (or build) the accurate load.

When I pull out the 220 Swift on a prairie dog town I’m not looking for 22-250 performance, if I was I’d shoot a 22-250. I want a load that shoots accurately at top velocity, I’m not looking for any “sweet spot” somewhere below safe maximum pressure/velocity. I also want the extreme spread velocity to be as small as possible. On a calm morning, when I crank the elevation knob 18 clicks up and put the crosshairs on a tiny target “way out yonder” the difference between 3865 fps and 3925 fps is a vertical miss. I’m gonna use the chrono to find the highest velocity load with the smallest ES (and to a lesser degree SD) that meets my personal accuracy standard for that rifle. I’m looking for a load with a minimum amount of vertical stringing “waaaay out yonder”, with FULL velocity performance.

If I’m working on midrange cast boolit revolver load, I’m looking for something insensitive to powder position. I alternate between muzzle down/muzzle up between each shot, the chrono will tell me in short order if I need to change something. For me, this is more important with a single action revolver because I use a loose hold and allow the grip to rotate in my hand. Changes in velocity = changes in recoil = vertical stringing even at short range. I can tell during initial bench testing that this load ain’t gonna work for me when shooting “free hand”, before I shoot it “free hand”.

I don’t think the chrono is gonna find “the accurate load”, the barrel has to like the bullet, or boolit. You could build a load with ES 10/SD 5, but if the gun doesn’t like the projectile it ain’t gonna matter. But if the barrel/projectile like each other, than the chrono can be used to “tweak” things in order to lower ES/SD/MAD. Isn’t consistency important to accuracy? Consistent powder charges, seating depth, neck tension, ignition, alloy, diameter, whatever.... Well I got’a believe consistent velocity sure ain’t gonna hurt. I put a lot of stock in low extreme spreads, I’d say at least 80% of the time, my most accurate load for any given gun is the one with the lowest ES/SD/MAD. The chrono doesn’t “find” the accurate load, but it sure speeds the process by quickly eliminating the (or my personal) unacceptable. A change in the load may not make any difference in group size at 50 or 100 yards (like maybe the primer), but if it makes the velocity more consistent, in my book I’ve improved the load. I know the improvement will make a difference at some point, even if I’m not aware of it at the time.

Do you need a chronograph to develop an accurate load, or find the maximum load, or....? NO, absolutely not! But a chrono does move your load development from a two dimensional world into a three dimensional world, and considering one can be had for less than the cost of some lead pots..... Well, why not have one? And why not use the heck out of it?

S.B.
03-15-2008, 09:00 AM
Now, I'm confused. Usually, I just look for consitency in the loads?

Larry Gibson
03-15-2008, 12:45 PM
Larry,
Here's the point I'm interested in that I think you make.
If we start testing at 100 yards; accurate consistent loads are better L.R. candidates than accurate inconsistent loads.
The LR big bore guys tell about the more accurate higher ES load (at 100 yards) being LESS accurate at L.R. than the less accurate lower ES load (at 100 yards).
This is the part of what you've said that's I'm interested in here; if I've got it right.
joe b.

Yes, that is also what I said. A 2 MOA group with a low ES and consistant SD will out shoot a 1.5 MOA group with a large ES and lowSD every time at long range.

Larry Gibson

crabo
03-15-2008, 02:32 PM
Whitespider, thanks for that post. I have been reading all the posts, but always got lost in the math and what you said makes sense.

Crabo

Maven
03-15-2008, 06:13 PM
joeb, I can offer nothing to Whitespider's eloquent response except to say that using a chrono. may speed up the load development process. It will also give you as much data as you need to make a meaningful decision regarding Load A v. Load B, but your targets, at various ranges, of course, may well be the deciding factor. Sorry that I can't add more to this topic.

Maven
03-17-2008, 07:46 PM
After my last post, I wondered how Lyman determines the potentially most accurate loads for their reloading manuals, thinking they'd use or need a chronograph to do so. Here is their reply to my e-mail:

"The accuracy loads are the loads that gave us the most uniform ballistics during our testing. This would include both pressure readings and chronograph readings. Generally, the most uniform loads will provide some of the best accuracy. The loads are not however actually shot at a target."

----- Original Message -----
From: "lyman1" <lyman1@lymanproducts.com>
To: <custsvc@cshore.com>
Sent: Friday, March 14, 2008 12:36 PM
Subject: Data posted to form 1 of http://lymanproducts.com/Contact.htm


Hmm, both pressure and chronograph data are necessary, but a target is not. Who'd a thunk it?