Having a brain freeze this morning. Got a new Chrono (first one) and I know you want the SD to be as small as possible but how is it computed and what does it mean? Thanks, Wayne

Without getting too complicated.

Average (the mean) doesn't tell you anything about the extremes of your set of numbers. If you have two number (2,38) the average is 20. But if you have two numbers (18,22) the average is still 20. From the average you can't tell which set of numbers were more consistent. (Think in terms of the velocity of your reloads). One way to differentiate is called variance. You take the square of all the differences from the average. And then figure its average. So in the fist case the differences are (-18, +18) their squares are, (+324,+324) and their average is 163.5.

Now that's a rather scary number the square takes the variance and you get 12.8. The Std Dev. In the second example, differences are (-2,+2), squares are (+4,+4), Variation is 4, Std Dev is 2.

NOW WHAT IT TELL YOU IS: If the velocities have a "normal" distribution (think bell curve), the Std Dev would tell you that 68% of them would be +/- 1 Std Dev from the average. And the 99.99% of your data is +/- 4 Std Devs from the average. (EXAMPLE 1000fps with a Std Dev of 20. 99.99% of the shots will be within 920-1080fps) What you have to ask yourself is, "Is that okay to have that big a difference in my shots? Accuracy wise? Pressure wise?"

For a tactical handgun, it might be okay. For a benchrest rifle no way.

Hope that helps.

Alf
(And hope I got my math right)

Oops. I knew I'd make a mistake. In the second full paragraph that should read,


Now that's a rather scary number, so take the square root of the variance and you get 12.8. Whis is the Std Dev. In the second example, differences are (-2,+2), squares are (+4,+4), Variation is 4, Std Dev is 2.

Alfsauve: Thanks for the reply -

quote:

So in the fist case the differences are (-18, +18) their squares are, (+324,+324) and their average is 163.5.

I follow up until you say the average is 163.5. How is the average of +324 and +324 come up to 163.5?

quote:

In the second example, differences are (-2,+2), squares are (+4,+4), Variation is 4, Std Dev is 2.

Seems like you did something different in the second example.

Alf, what a great explanation. You should think of taking up a career in teaching math - if you don't already.

- mike

quote:

but how is it computed and what does it mean? Thanks, Wayne

How it's computed is complicated.....what it means isn't

It's simply a numerical method of measuring variation! The smaller the standard deviation the more consistant your velocities are! Simple.

Standard deviation should mostly be ignored unless they become very large....such as SD of 50. A SD of 15 isn't bad at all. It means your extreme velocities run +/- three times that or 45. A SD of 50 means your extreme range of velocities runs about +/- 150'/sec. BTW....it's very unlikely that you will ever actually see the total variance in velocity as usually we see only 2/3 of it because we don't throw hundrds of rounds over the chrony.

IMO the shooting world would do fine without using the SD at all.

Thanks guys. I read these and some previous posts and it all seems to fit together. No longer concerned how to calculate it since the SD is given by the Chrono. My use and interpretation of the SD (for what it is worth) I now have a better understanding of. Wayne

Quoting Zediker:

"A tolerable sd is 12. Anything more than that is not good; anything less than that probably doesn't perform any, if at all, better than a twelve."

Consider this to be the empirically derived opinion of a High Power shooter.
.

quote:

I follow up until you say the average is 163.5. How is the average of +324 and +324 come up to 163.5?

Aerostarp: You're right I knew my math was going to be off. The average of a set of two numbers, both 324 is of course, 324.....duh.

The sqrt then is 18. Which is the std dev.

The long and short is as, Vapodog said. We really don't take a big enough sample to allow us to put a LOT of stock in our Std Dev numbers. It is wise, if the number is really high to ask yourself why. Different cases, different primers, inconsistent powder chargers. Or as in my case lately, I was too close to the screens!

Alf

Thanks Alf:

I will use the SD more as an indicator rather than an absolute value. Appreciate everyone's input. Wayne

JMHO Standard deviation is more important the longer distances that you shoot. A difference of 200 fps between two shots at 100 yards isn't going to mean anything at the target. At 1,000 yards it will mean a difference in trajectory of feet.

The 308, 168 grain match bullet at 3,000 fps drops 329" at 1,000 yards. At 2,800 fps the drop is 379" for a trajectory difference of 4+ feet.

If the muzzle velocity difference is 20 fps versus 200 fps the trajectory difference would only be a couple of inches.

Even though both loads average 2,900 fps the smaller SD will always shoot better.

One must actually look at ES along with SD. I have been chronographing since '75 which gave ES and since '89 with a M35P which gives ES and SD. I have seen SDs that were very small alongside a large ES. Such is not a good load and most often produces "flyers". It is also indicative of inconsistant ignition. Conversely I have seen loads give excellent accuracy out to very long range that had small ES with a proportionally large SD. Ideally what I look for is a low ES with and SD that is 20-40% of the ES. Such loads have proven to be the most consistantly accurate loads over short and long range in a multiple of cartridge/calibers.

Larry Gibson

quote:

Originally posted by vapodog:

quote:

but how is it computed and what does it mean? Thanks, Wayne

How it's computed is complicated.....what it means isn't

It's simply a numerical method of measuring variation! The smaller the standard deviation the more consistant your velocities are! Simple. ...IMO the shooting world would do fine without using the SD at all.

Absolutely correct and the best answer of the bunch.

Hang the Targets out at 300-400 and see which Loads give the best groups. Those are the ones to use and will be the ones closest to the Harmonic Node. And as a nice benefit, there is no need to totally waste your time messing around with the chronograph.

SDs, ESs and Velocities may impress the Beginners, but it doesn't mean spit if the groups aren't consistently tight.

Good Hunting and clean 1-shot Kills.

For a quick and easy calculation of SD, look at this: http://www.physics.csbsju.edu/stats/cstats_NROW_form.html

Just put in as many data values as you like using the Tab key to jump from one box to the next (ten is a good start), then click on the Calculate button. You will instantly get a slew of values telling you statistical things about your data.

I found another site like this a while back, but can't find it now. It gave hi, lo, es, sd, avg, mean and some other value that I did not understand. Use it in good health...

I like to say that SD is a numerical way to describe the "sameness" of the data values. Imagine 99 shots fired at 3000 fps and one at 5000 fps. The SD of this string would be very low because the one 5000 fps shot is such a small deviation in velocity from the majority of shots. Now imagine two shots at 3000 and one at 5000. The SD of this string would be very high because of the one 5000 fps shot being so "unsame" from the other two shots.

Has anyone found a corrolation between a reasonable velocity spread with just the odd one deviating a lot to a reasonable group with the odd flyer?

How about a wider SD and differences in primer flattening? (Not all primers are equal - I get some that are hard to seat and decap. Other than that, they all look the same when fired, but distinctly different when the load is changed).

quote:

Originally posted by 303Guy:
Has anyone found a corrolation between a reasonable velocity spread with just the odd one deviating a lot to a reasonable group with the odd flyer?

HUH?

I don't understand your question, but the answer may be to throw the flyers out of your calculations.
.

303guy

I mentioned the correlation in my post.

Larry Gibson

You did indeed Larry Gibson. Now that I have read it more carefully! (I was still on my first coffee).

Winchester 69, what I meant was, is it the shots with more extreme deviations in velocity that open up the group? But I didn't read Larry's post properly - he already said so!

Actually, after reading Larry's post for a third time, I have realized that he has made a huge statement there. Just look;

quote:

Ideally what I look for is a low ES with and SD that is 20-40% of the ES. Such loads have proven to be the most consistantly accurate loads over short and long range in a multiple of cartridge/calibers.

It took a while to sink in!

So why do I shoot test groups without a chronograph? Well, for a start I didn't know ....

Folks, isn't this kinda akin to the folks that do a labour intensive case prep BEFORE they ever shoot and fire form the cases?
I mean, you are ultimately looking for bullets that go thru the same hole. If you acchieve that, then the ES and SD become moot. And pretty well take care of themselves. I've never heard of a stool shooteer yet that shot a 3" group and said "yeah, but I've got my SD down to 3fps".
I think all of this got started by some rag writer as a Phillip Space thing. And, of course, before every kid on the block had a Chrony, it wasn't heard of and they did some pretty good shooting back then. Now things have changed and it's something for the gadget heads to measure. Why? Because we can.

Fjold:

You have got to change your Avatar - I can't ever seem to concentrate on anything you write.

Wayne

quote:

Or as in my case lately, I was too close to the screens!

Alf

Yeah, that's the other thing about chronys. I was measuring muzzle blast there for a while until I got my act together.

And no matter what anyone tells you --- shooting for the chrony is a BENCH RESTED deal. If you question why, just Google "I shot my chrony!"

I would also add the if you calculate the SD of say 5 shots it's pretty worthless as a statistic. The more shots you measure the more the SD is statistically relevant.

Benchrester are already using componants and loads that well known to give consistant ignition. Most often they are simply "tweaking" loads, not developing loads.

The chronograph and knowing the ES and SD is very useful in the development of loads. It lets you quickly select the most uniform loads for further testing. It also lets you eliminate those loads that may group well at 100 yards but yet have a large ES and/or SD, a load which would prove inaccurate at longer range. Loads shooting well at 100 yards (1 - 1.5" moa) are more common than many think.

Since most load development is most often done in 5 shot strings the measurement of velocity, ES and SD is not a "pretty worthless statistic". While I've had loads that initially gave small ES/SD but further testing proved them to actually give large ES/SDs. On the contrary, I've never had a load that gave a large ES/SD give a smaller one on further testing. Thus the chronograph lets us select loads that are performing at a velocity we expect and to eliminate loads that are doing what we want or are inconsistant. Componants are saved, barrel life is saved and our own time is saved because we can focus on what is working without further effort wasted on what's not working.

Larry Gibson

quote:

Originally posted by Wink:
I would also add the if you calculate the SD of say 5 shots it's pretty worthless as a statistic. The more shots you measure the more the SD is statistically relevant.

Excellent point Wink.

Some folks do enjoy monkeying with the (mostly worthless) accessories that go with Reloading to the point that they really loose sight of what is important. They can quote you numbers until the cows come home that make them feel better about having wasted a lot of money on whistles, bells and trinkets.

I've always enjoyed shooting against the Chronograph Commandos.

Aero,

one would think that the load with the lowest SD spread would be the most accurate....

Sometimes it is, and sometimes it isn't....

Did a big time load testing with a 6mm Rem a few years ago, with the 75 grain Hornady HP and the 115 grain Berger to be the 2 most standard bullets to be used in that rifle..

Both bullets were tested with 15 different powders...along with various charges....

the 75 grain HP was the one showing the wider swings in SD....the worst one was with H414, as it was producing velocities with the same charge from 3600 fps to 3750 fps with the same bullet, same charge ( 47.5 grains) and multiple brand of primers were tested...the velocity swing was that extreme across the board....

however out of the 15 powders tested also.. that charge of H 414 was the most accurate... it turned in several groups at 100 meters that measured .0505! Kid ya not...

So as Hot Core calls the believers in chronys as Chronograph Commandos.. I think there is a valid point there... go what is accurate in your rifle.. MV variations may play a part when you are shooting at 1000 yds or so...but under a lot of circumstances, a chrony should be used as a last resort in load development, by letting you know what THAT load is averaging, in THAT rifle... and you can set your sighting set up according to that and what your needs are...

but a chrony is only a minor indication in accuracy potential...

in my beloved or hated Blue Dot loads, BDot gives minor variations in SD for velocity... and its accuracy potential is pretty indicative when comparing the smallest deviation.... but then you look at H 414, and that whole theory is right out the window...

Thanks Seafire. I pretty much was just curious about SD and it's application to what we are doing. The results I see on the target are my number one indicator as to accuracy. I only have access to shoot at 100 yards for target shooting so perhaps the ES and SD would prove more valuable to someone who shoots long distances. I was really surprised at the much higher velocities I was getting from my loads than published in the manuals. Wayne

Yeah, but I still want to know what my loads are doing. At the moment I am still 'estimating'! Someone I know must have a chrony! - that hasn't been shot!

Anyway, Hot Core, you make it quite plain that you have no time for a chrony - BUT, hey, doesn't it make reloading more fun?

quote:

Originally posted by aerostarp:
Fjold:

You have got to change your Avatar - I can't ever seem to concentrate on anything you write.

Wayne

Are you kidding????

No offense Frank.. but I read everything you post... never know what it said, but I look for everything you post....

never cared for basketball, but I LOVE those basketballs dribbling down the boulevard...

quote:

Originally posted by 303Guy:
...Hot Core, you make it quite plain that you have no time for a chrony - BUT, hey, doesn't it make reloading more fun?

Hey 303Guy, What makes me the most upset about it is that "" I "" used to WASTE TOTALLY WASTE a lot of my time shooting across a Chronograph. I got duped into thinking I was actually gaining something worth knowing, and I detest getting fooled.

It began in the CORPS when I had access to the old "Break-a-Screen" design. Shoot a Bullet through the Screens and you knew a Velocity. Record a bunch of them and hand calculate all the (worthless) statistics you could ever possibly imagine. Then have a Gunny walk in ans ask, "How does it shoot?" Which immediately realigned the Priorities to the proper order.

Time passes, get fooled by the gun rags into thinking (again) there is something to be gained by using a Chronograph. Begin chronographing all kinds of Loads. Plenty of numbers - PLENTY!

Shooting over the Chronograph one day and an older (and in retrospect much MUCH wiser fellow) walks down and asks how it is going. Told him fine and thought he wanted to use the chronograph. Then he used the same basic logic the Gunny had previously used, "No thanks. I'd rather see how they actually shoot - at longer range."

Well duuuuuhhhhh!!! The wisdom of the Elders came through again.

Since then the only time I wasted with a chronograph was helping a buddy get it set up so he could use it. No doubt about it, a chronograph will "often"(but not all the time) tell you what the velocity is for a Bullet/Load/Firearm and the ones available today can indeed crank out plenty of statistics.

The disgust I often post about the chronographs is actually aimed at the time I wasted. I HATE being duped. If anyone can learn from my mistakes, good for them.

quote:

As Seafire said:
one would think that the load with the lowest SD spread would be the most accurate....

Sometimes it is, and sometimes it isn't....

Those are words of first-hand experience, which a lot of the Beginners simply don't have enough Trigger Time to have seen. The same nimrods will argue that the Chronograph tells all you need to know. If they keep at it though, the reality eventually sinks in. Welllll..., some(I have one in mind) will never figure it out.
-----

So, if your "quest" is for low statistical numbers, the Chronograph is the way to go. It will tell you the "numbers". And the Chronograph Commandos can regail all the Rookies and Beginners with the - Ta Da - Numbers!

If on the other hand you are interested in locating the best Harmonic Node which will produce the Best Accuracy, then the Chronograph simply is not needed. That does not mean it is worthless though, they do stimulate the economy when they are purchased.
-----

I HATE being mislead, flim-flammed, fooled, PT Barnumed, tricked, suckered-in.

I'm gonna disagree that a Chrony is worthless. It has it's place like any other tool we use. It's when folks try to turn it's use into some sort of doxology that you run into problems. It is not the do-all be-all? No. But it does give me information that I can use.
Knowing what your bullet is doing is a tremendous asset in and of itself. That is indisputable.
And, of course, we rookies and beginners have to spend our money on something. I mean once we learn from you that we can reload with a rock and a sharp stick every once in a while we like to buy something new and shiny.

The best of all worlds for a reloader is to shoot many rounds, period. You can shoot without a Chrony and figure out what you want, you can shoot with a Chrony and figure it out much faster, but once again you must shoot, shoot and then shoot more. With a Chrony you need to shoot many samples before you draw conclusions, shooting without a Chrony may also require shooting many samples, possibly more than with the Chrony. ----- I shoot 3000 plus rounds per year, 90% of them with a Chrony. If you shoot enough you someday will shoot a 0 SD. I have done it with five of my rifles. Two .358 STA's, a 7mm STW, A .338 Lapua and a .257 Wby. Those loads that I shot the 0 SD with required many shots researching and tweaking until achieved and will get you that one holer you want. When you shoot a 0 SD you will find a very accurate load, and from then on you can count on that load. You will also find that YOU are the big variable in your shooting, not you load or equipment, be it Chrony or whatever. Those that don't use a Chrony enough are in for a revelation, it can be a very informing tool for the serious shooter, regardless of the chambering shot. That said, some of the best shots I know have never used one, but they shoot enough to know what their loads are doing. This is my .02 worth, with thousands of rounds fired over the years. Good shooting.

quote:

If you shoot enough you someday will shoot a 0 SD.

See Hot Core, I knew there was fun to be had!

I have only ever used a homemade break screen chrony - I still had to convert the counter to seconds. Then I only used it see where I was at. My 303 was giving me 2390 fps with a 180gr RN and 2690 fps with a 150 spire point. My mini-14 was giving me 3100 fps with 55 grainers. And that was it. (Other than determining that I had fired 500 rounds of flipping machine-gun ammo through my 303 - a 1902 model complete with dust cover. Oh yes, my Dad's 303 gave a lower velocity with the same load and a shorter barrel). But it was fun just knowing! Ahh ... let me not forget - I was getting an extreme spread of 6 fps with the 303 and something equally impressive with mini-14. I put it down to a good powder (same powder in both) that being MR200 (no typo's).

Hey, wait a minute! 0 SD!!! Holy smoke !!!!! I would want to know I achieved that !!! That must have taken some doing!

quote:

Originally posted by stillbeeman:
... we rookies and beginners have to spend our money on something. I mean once we learn from you that we can reload with a rock and a sharp stick every once in a while we like to buy something new and shiny.

That is as good a reason as knowing the (worthless) "Numbers". And someone did mention buying them does help stimulate the economy.
-----

Hey 303Guy, Take a 2x4 and put a piece of Tape on the end it about the size of a CC's (Chronograph Commando's) LED Screen. Mount it to a Tripod and write " 0 SD " on the Tape. Dangle a bunch of wires from it and tape them to the outside of a portable Radio. Turn the radio on Low and shoot across the 2x4.

Now you can get all the " 0 SD " reading you desire. And while the barrels are cooling you can have the radio to enjoy.

For Velocity, simply Average the Velocities shown in a couple of Manuals for the "approximate" Load, subtract 150fps and you will normally be real close to reality. Even if you aren't, it doesn't mean anything. Or..., you can actually add 400fps with this excellent method if you want to have a Fast Barrel to impress the Beginners with.

The reason it doesn't amount to anything, is you still have to actually shoot your rifle at the distances you intend to take shots and create your own Drop Chart. The CC - Computer Generated Trajectory Table - "might" get you on paper, but it certainly can not be counted on to represent the flight path of a specific Load in a specific firearm, even though some of the rookie CCs think so.
-----

I've been working on a way to calculate Kinetic Energy with a given Load and a Chronograph that is actually meaningful. It has to do with "how far" a Chronograph is tossed after a CC blasts it.

As our old and wise buddy Tnekkcc says, "What does it all mean?"

If a person "thinks" he gains something from shooting across(or through) a Chronograph, then he should do it.

But it sure isn't needed to create Accurate l-o-n-g distance Loads.

Sorry, taking numbers from various load books and averaging them is not data; shooting bullets over a Chrony and averaging their velocity is data. And that data is bullet specific and rifle specific.
I've never developed a loooong range loading. I don't shoot looong range. I don't hunt loooong range neither. But a Chrony helps me know the dynamics of what is happening in my cartridge when I am shooting short range. I agree that SD and such are just numbers that we measure "because we can", but there is quite a bit more to a Chrony than that. Just like you can load powder with a bowl and a spoon, a Chrony isn't a must have item, but properly used it certainly makes you a better reloader.
Plus, of course, when I bought mine for @ $80 about 20 years ago, it was new and shiny.

I want to know the 'truth'. You see, I imagine my loads are real fast! I don't like 'flim-flamming' myself!

But seriously, I really do want to know what is making my loads tick. I already know that they are just not going to cut it as a looong range load (pity, because our local service rifle club shoots a fair distance). But I do know I can smack a magpie in the chops at 175yds. Well, in the middle of the chest, anyway. Now all I have to do is learn how to estimate distance! (The GPS only works after I shot 'em).

quote:

Originally posted by stillbeeman:
Sorry, taking numbers from various load books and averaging them is not data; shooting bullets over a Chrony and averaging their velocity is data. And that data is bullet specific and rifle specific.

Gotta agree and well said for a CC. Gotta love them "statistical numbers" However..., for all the Beginners, the good old "guesstimation" works just as well, and you can do it at home.

quote:

I've never developed a loooong range loading. I don't shoot looong range. I don't hunt loooong range neither.

Nothing wrong with that. I like being up-close to the game myself. When you can sneak in and out without upsetting the woods/swamps, you have done real well.

quote:

But a Chrony helps me know the dynamics of what is happening in my cartridge when I am shooting short range. I agree that SD and such are just numbers that we measure "because we can", but there is quite a bit more to a Chrony than that.

Again we agree. You can add - cost and hassle - to the more to it

quote:

Just like you can load powder with a bowl and a spoon, a Chrony isn't a must have item, but properly used it certainly makes you a better reloader.

quote:

Plus, of course, when I bought mine for @ $80 about 20 years ago, it was new and shiny.

Shiney economy stimulus - with the economy the way it is, it would be a good time for you to buy a Spare.
-----

Hey 303Guy, I've come up with a Cost Reduction which increases the Reliability and lowers the hassle factor.

Take a picture of the 2x4 with " 0 SD " on it and tape it to the front of your 3-ring Load Data Manual. You will still need to run the wires down range from the flick for some distance - not closer than 15' so Muzzle Blast does not affect it - and back to the radio. That way no Tripod is needed.

When folks ask, "How does that thing actually work?" You can smile, shake your head, and tell them the wires pick up what is Technically refered to as"Bullet Shock-wave induction" which send that info to the radio and flick. Or you can shorten it to simply good old BS.

Well, I like mine. It's cute. And shiny. And fun. If you spread $80 out over 20 years, it's a lot lower maintainance than a hot blonde. And it hasn't developed any wrinkles. Nor an attitude. If I decide to get the latest model wtih the built-in radio so I can listen to Hank Williams Jr sing "Are you ready for some football" whilst my rifles cool, the old one won't pout. If it does, I'll just shoot it. And its still been a cheap date. So, neener, neener, neener.

The numbers are not worthless; they provide much factual information. Hot Core knows it all so I understand why he does need to know “the numbersâ€. Perhaps his experience with “break a screen†chronographs soured him on them. They were slow but the info was still there. To him a waste of time, to the rest of us valuable time spent. But then skyscreens have been around since the early ‘70s. Maybe Hot Core should come out of the dark ages. I haven’t used a “break a screen†chronograph since ’75. Ignorance is bliss I guess.

Larry Gibson

quote:

Originally posted by phurley5:
If you shoot enough you someday will shoot a 0 SD.

Mr. Hurley, I would challenge that statement. If you measure enough shots with the same load, on the contrary it is almost impossible to come up with an SD of 0. Hence my remark about calculating the SD on a small number of measured shots. I refer anyone who has one to read the section on standard deviation in the Speer manual, or this:

http://www.shootingsoftware.com/ftp/Perverse%20Nature%20of%20SD.pdf

quote:

Originally posted by stillbeeman:
Well, I like mine. It's cute. And shiny. And fun. If you spread $80 out over 20 years, it's a lot lower maintainance than a hot blonde. And it hasn't developed any wrinkles. Nor an attitude. If I decide to get the latest model wtih the built-in radio so I can listen to Hank Williams Jr sing "Are you ready for some football" whilst my rifles cool, the old one won't pout. If it does, I'll just shoot it. And its still been a cheap date. So, neener, neener, neener.