Ordered a Chronograph and not really sure what to look for. I have several 223rem bullets sitting aside to be tested with Varget and figured I would wait until the chronograph got here sometime next week. I see guys talking about SD and other things. I know the basics like shoot through the screens/V but haven't a clue what the data means.
How to use a Chronograph.
- Thread starter Axis II
- Start date
- Status
Mark_Mark
Member
- Joined
- Jan 9, 2021
- Messages
- 17,944
GeoDudeFlorida
Member
- Joined
- Dec 1, 2020
- Messages
- 11,055
I've had three (four mebbe?) Chrony F1's. No longer made. When this one takes a bullet or gets rained on because I forget and leave it open and powered on at the berm, I'll have to buy a different model. I'm all out of spares.
One thing about the new chronographs (from what little I've seen) is they're WAAAAAY over complicated for "the average" handloader. One of the BR guys at the outdoor range has one that tells you the temperature and atmospheric pressure, along with velocity, string and shot averages by rank, SD, ES, 1/2/300 meter deltas, the time in Hong Kong, local gravitational flux, how many licks it takes to get to the center of a tootsie pop... all kinds of things (okay, I might have made up the part about atmospheric pressure...) but it's kind of a data overload type situation if you just want to know how close you are to book velocities for a given load.
He had to buy a new laptop to hook to it because his old one didn't have a fast enough USB port. Another guy's got one that talks to his cell phone.
GeoDudeFlorida
Member
- Joined
- Dec 1, 2020
- Messages
- 11,055
You would know about deviancy...
Bearded Phil
Member
Standard deviation in mathematical terms for the layman is the value that represents how closely numbers in a set are to fall within the mean average of a set of numbers.
For example, take this set of 5 shots that I chronographed:
1061
1077
1072
1069
1075
The average for these 5 shots is 1070.80
The standard deviation for these shots is 6.26 (sample standard deviation, look it up if you want a deep dive into the two different types but know that chronographs use the "sample" SD method)- edited to correct type of SD used (not population SD)
The spread of low to high for all recorded shots is 16
So the data tells me that by standard deviation that my shots with this powder, bullet, primer combination with all other factors being as equal as possible, including weather conditions are likely to fall within 6 FPS of the average of 1070 FPS.
This is useful for finding a powder charge that can potentially be the most accurate. This is not always the case though so be weary, most chronographs have you record the FPS at around 12-15' from the muzzle. What they can't tell you is what eventually happens to your point of impact down range, you'll have to find that out by shooting at targets and chronographing together. A load could have very low standard deviations and spreads of velocity but be not as accurate as another load that has slightly higher SD & ES (extreme spread).
For example, take this set of 5 shots that I chronographed:
1061
1077
1072
1069
1075
The average for these 5 shots is 1070.80
The standard deviation for these shots is 6.26 (sample standard deviation, look it up if you want a deep dive into the two different types but know that chronographs use the "sample" SD method)- edited to correct type of SD used (not population SD)
The spread of low to high for all recorded shots is 16
So the data tells me that by standard deviation that my shots with this powder, bullet, primer combination with all other factors being as equal as possible, including weather conditions are likely to fall within 6 FPS of the average of 1070 FPS.
This is useful for finding a powder charge that can potentially be the most accurate. This is not always the case though so be weary, most chronographs have you record the FPS at around 12-15' from the muzzle. What they can't tell you is what eventually happens to your point of impact down range, you'll have to find that out by shooting at targets and chronographing together. A load could have very low standard deviations and spreads of velocity but be not as accurate as another load that has slightly higher SD & ES (extreme spread).
Last edited:
twarr1
Member
You don’t need to know the intricacies of statistics. Lower Standard Deviation (SD) is better. General consensus is 15 or lower. I like to see single digit and preferably less than 5. Of course, the bigger the dataset the better.
People use velocity as a proxy for chamber pressure, but it’s a poor substitute. This has been known for over 100 years. Absolute velocity is basically useless. Relative velocity can be useful. (Shot to shot). Charting relative velocities can reveal a curve of diminishing returns or a ‘plateau’ where small increases in charge don’t result in increased velocity.
You can go down a rabbit hole with data or you can measure for consistency. How far you get into charting, statistics, etc is up to you based on your level of interest.
P.S. Eventually you will probably shoot the chronograph. Don’t feel bad. It happens.
People use velocity as a proxy for chamber pressure, but it’s a poor substitute. This has been known for over 100 years. Absolute velocity is basically useless. Relative velocity can be useful. (Shot to shot). Charting relative velocities can reveal a curve of diminishing returns or a ‘plateau’ where small increases in charge don’t result in increased velocity.
You can go down a rabbit hole with data or you can measure for consistency. How far you get into charting, statistics, etc is up to you based on your level of interest.
P.S. Eventually you will probably shoot the chronograph. Don’t feel bad. It happens.
markr6754
Member
Nice....well stated, except that the population SD computes to 5.6, while the sample SD computes to 6.26. The difference is quite small, but it's there. It still boils down to a likely 6 FPS range from the average.
Otto
Member
- Joined
- May 14, 2007
- Messages
- 2,355
Extreme Spread(ES) To get the Extreme Spread, the lowest velocity (for the current string) is subtracted from the highest velocity.
Standard Deviation(Sd) Consider an example to illustrate the meaning of standard deviation. If for example you have a standard deviation of 10 fps with an average velocity of 1000, 68% of the shots you fire will fall within 990 to 1010 fps. If you double the 10 fps standard deviation to 20 fps, 95.4% of the velocities will fall within 980 to 1020 fps. The more shots you fire, the more accurate the standard deviation. A minimum of 5 shots is necessary.
Standard Deviation(Sd) Consider an example to illustrate the meaning of standard deviation. If for example you have a standard deviation of 10 fps with an average velocity of 1000, 68% of the shots you fire will fall within 990 to 1010 fps. If you double the 10 fps standard deviation to 20 fps, 95.4% of the velocities will fall within 980 to 1020 fps. The more shots you fire, the more accurate the standard deviation. A minimum of 5 shots is necessary.
Bearded Phil
Member
I may have gotten the population vs. sample mixed up. I looked up a standard deviation calculator to do some figuring when my chrono didn't record some shots but I noted down the FPS and found this one
https://www.calculator.net/standard-deviation-calculator.html
had to pump in some old data to see which type I should be using. You are correct, I meant to say sample SD above. Gonna edit that real quick.
Last edited:
Bearded Phil
Member
Also, yes. I'm on my second chronograph. You can imagine why. My tip on this: when you're chronographing handgun data (even when using a rest!) wrap it up before you get too much hand fatigue. I accidentally blasted mine with a .357 on shot 48/50
fxvr5
Member
- Joined
- May 26, 2017
- Messages
- 3,270
Nope. The spread is defined as the range of the lowest and highest measurement.
In statistics, the standard deviation is a measure of the amount of variation or dispersion of a set of values.
https://en.wikipedia.org/wiki/Standard_deviation
LiveLife
Member
I found more consistent the velocity readings, better the data.
Each chronograph will have recommended distance from the muzzle to eliminate muzzle blast readings to confuse the velocity readings. My Caldwell unit recommends 10'-15' and some recommend 15'-20'. Larger the muzzle blast, further away you need to be from the muzzle for "sky windows" on top of the chronograph to get accurate readings.
And the reason why you should be towards the bottom of the "V" is to get closer to the "sky windows" for the Chronograph to measure bullet traveling over to calculate velocities. Well, that means aiming closer to the Chrono but if you are concerned, you can always place a thick metal deflection plate to protect the Chrono as my Caldwell unit has remote readout wire that comes to the bench for my smartphone. (Some will replace metal "V" rods with wooden dowels so if bullet fragments from hitting the protective metal plate shatters the wooden dowels, no problem, replace them easily).
As some posted, having consistent lighting helps with more consistent readings as I found different reading variations from morning sun, full sun, overhead sun, cloudy and dusk conditions.
And since most powders are temperature sensitive (Velocity increases as temperature increases), I also note ambient temperature for chrono data but keep in mind that it's "powder" temperature and not "ambient" temperature that matters and if your chamber is hot, chambered round will get warmer so your velocity readings can increase with subsequent shots to mess up the SD/ES numbers.
(Why doesn't anyone tell me these stuff like warm round in hot chamber will throw off higher velocity numbers if left chambered too long! 
)So for more consistent readings, I keep my test rounds indoors kept at around 62F and if range conditions are too cold/hot, I will keep the rounds in the ice chest and allow sufficient warm up shots to warm the barrel/chamber then cool down to maintain more consistent barrel/chamber temperatures (Yeah, call me OCD).
fxvr5
Member
- Joined
- May 26, 2017
- Messages
- 3,270
Mark_Mark
Member
- Joined
- Jan 9, 2021
- Messages
- 17,944
that’s right Range! I was a QC lab and QC factory guy for a few years!
in my early 20’s! was BORING
I've often wondered how people actually shoot the chronograph.
Just looking for FPS for ballistic programs and consistency.
GeoDudeFlorida
Member
- Joined
- Dec 1, 2020
- Messages
- 11,055
Well, I'll tell ya, it always starts with buying one...
Soonerpesek
Member
GeoDudeFlorida
Member
- Joined
- Dec 1, 2020
- Messages
- 11,055
That's what we're here for.Why doesn't anyone tell me these stuff like warm round in hot chamber will throw off higher velocity numbers if left chambered too long!
gifbohane
Member
- Joined
- Nov 7, 2016
- Messages
- 1,180
I found it easy to do and did it frequently, I could even hit the support wires without trying. Gave up and bought a Labradar.
Should I take the ammo I worked up to the range and find what the gun shoots best and then chronograph or shoot each round of each charge through the chronograph? I loaded 5 of each from start to close to max going up 3 tenths of a grain each load.
.45Coltguy
Member
Probably for most shooters using a chronograph for the first time, MV/fps is all they really need or want. All the other stuff you can look at later, if interested.
.45Coltguy
Member
Is the rifle/scope zeroed? Don't want to work on zeroing shooting thru your new chronpgraph. Splat!
Bearded Phil
Member
I used to chronograph only when starting out but now I shoot over the chronograph at a target as well. Huge time saver.
- Status
Similar threads
- Locked
