How accurate is your chronograph?

[Treefrog]

Exactly….this is very true in the archery industry as well. Compound bows often end up short of manufacturer speed ratings and people will go nuts to find even 5-10 fps more speed.

Perhaps the bow manufacturers could fudge their numbers a little so that their products would actually exceed their customers' expectations. (Hannah Barron had that happen recently and I thought it was cool.) All marketing is just some form of psyop, so why not?

I just don't understand why it's SO important to everyone that things go faster. I watched a guy ruin a beautiful Colt 1911 at the range because he just HAD to get a certain bullet to a certain velocity. Well... He did. Once. That was the moment that he recognized his own incompetence. Luckily, he wasn't hurt. I've concluded that some reloaders shouldn't own chronographs because they're too easily lead into unsafe behaviors.

The little brother bought a break-barrel that's supposed to get to 1400-fps and he can't shoot it for beans, but he's happy with it. He doesn't understand why I can hit things with it, but then he's an engineer...

I think that in the end it all comes down to us and what we're actually capable of as shooters. A high-velocity miss is much less valuable than a lower velocity hit. Getting the average airgun buyer to understand that is where the problem lies.

Cheers,

J~

 

[Spartan]

Anyone can test the accuracy of their chronograph. You just need to compare the read-out results to an accurate ballistics table, and there are different ways you can do this. Either by measuring POI drops at known ranges or by measuring the speed difference at two or more different ranges, and then comparing that to the ballistics table. Certainly best suited to be done with high-quality rifle rounds where the manufacturer has stated a specific (and accurate) BC value, otherwise the user would have to determine BC on their own, which can also be done.

 

[Hold_Over]

Like most I use mine to measure consistency and variation before and after a mod/adjustment. I could see being much more in tune with precise accuracy in measuement if in a location with a 12fpe regulation. Don't wanna be over the line because of improperly calibrated equipment if you get checked.

 

[GeneT]

A huge amount of the variation in chrono readings (and let's admit it, they're tiny, and normally inconsequential variations) relate to the setup, rather than the instrument. Electronics are fast. Blazingly fast relative to the flight of a pellet, or even a high-velocity powder-burner. BUT deviations in how you place the screens of optical chronographs (is the spacing *exact*? Are you shooting through them such that the tangent of your trajectory intercepts the mid-line of the space between them? Are they aligned downrange, not just left to right, but vertically as well? Is your rifle?). Is your radar chrono exactly at the muzzle? (of course not) so there's some error due to angle. There are probably other sources of error with radar, but I'm not skookum enough with that tech to know what they might be.

In any case, the variations we're discussing are *tiny*. I've owned at least a dozen chronos and done a lot of comparisons. Bottom line they all measure very closely, except for Pact which for some reason was always about 10fps faster than my other chronos (Oehler, CED, Shooting Chrony (when it registers), Labradar (and by extension Garmin, which agrees closely with my LR even though I never checked it directly against any of my Pacts).

Short of unit comparison I don't think there's any standard you can use to make, say a NIST-traceable velocity measurement that's within the grasp of even a well-heeled airgun shooter. But velocity isn't the only measurement that falls into that category.

It's probably worth noting that you're also measuring an average velocity across some distance, so the whole thing is an approximation. No projectile travels at a constant speed during any of its flight.

GsT

 

[dgeesaman]

A chronograph Is a device that measures speed. Most all measuring devices or tools can be checked or calibrated in some way by using what’s called a standard that’s traceable to NIST
(The National Institute of Standards and Technology)
My question is how do YOU know if your chronograph is actually functioning accurately? Do you even know if it’s accurate when it’s new? How do you check your chronograph to make sure it’s accurately reading true?

Does a NIST traceable chronograph exist?

And why would it matter - it’s not like a slightly out-of-spec chronograph is going to mean much. Our ballistic models are still only approximations and shot to shot variance is much more significant.

The chronograph accuracy studies I’ve seen have compared commercially available chronographs against each other and the good ones are within 1% of each other. It would be a huge undertaking to do more rigorous comparisons (calibrations) than that.

I myself own a LabRadar, Bulletseeker, and two ProChronos and comparing them has never much mattered.

 

[Ezana4CE]

My main concern it to know within which range(s) projectiles are accurate and to measure FPE for hunting purposes. I have no idea how to calibrate a chronograph. Had not thought about it prior to this post.

 

[Struckat]

Like most I use mine to measure consistency and variation before and after a mod/adjustment. I could see being much more in tune with precise accuracy in measuement if in a location with a 12fpe regulation. Don't wanna be over the line because of improperly calibrated equipment if you get checked.

Interesting comments. It made me wonder what they do across the ocean?

Do the pellet speed cops use a chrony? I see post about tuning to the edge of regulation. I wonder how it’s checked.
Normal difference in instruments could get a person in a lot of trouble if shooting close to the limit.

 

[Hold_Over]

Interesting comments. It made me wonder what they do across the ocean?

Do the pellet speed cops use a chrony? I see post about tuning to the edge of regulation. I wonder how it’s checked.
Normal difference in instruments could get a person in a lot of trouble if shooting close to the limit.

At a guess. I would tune to 11.5 fpe and count on the 1/2 lb variation To compensate for off chrono readings and variations in temp.

 

[cavedweller]

Here’s another very good question that’s never talked about. I just brought up the reality that chronographs are not tested truly. Now throw in the variables of temperature, altitude and humidity for the gun. When somebody does a review on a gun or a customer purchases a gun from a retailer then shoots it over their chronograph and getting mixed results should they blame the gun for not performing to their chronograph readings and practices?
I’m totally in line with JD’s answer to this so far. And with that being said why are soooo many people so anal about their chronograph readings?

i have three different chronos, the new Garmin, the FX pocket, and the bigger FX newer gen.. I have 4 if you count the onboard chrono in my alphawolf. They are all within a few fps of one another.
I'm mostly concerned with staying legal for field target.
Sometimes with the Alphawolf, i'm interested in seeing if faster pellet speeds open a group or tightens a group, so... there's that
Since I'm not a tuner nor tweaker i mostly rely on Awesome Airgun Techs wisdom ... after that speed checks happen when i go to a competition where they usually chrono the gun.

 

[Chris_K]

Anyone can test the accuracy of their chronograph. You just need to compare the read-out results to an accurate ballistics table, and there are different ways you can do this. Either by measuring POI drops at known ranges or by measuring the speed difference at two or more different ranges, and then comparing that to the ballistics table. Certainly best suited to be done with high-quality rifle rounds where the manufacturer has stated a specific (and accurate) BC value, otherwise the user would have to determine BC on their own, which can also be done.

The POI drop is the only way I can think of for the layman to be able to judge the accuracy of his/her chronograph. I remember in high school physics class we calculated the velocity of suction cup dart guns doing this.

 

[LDP]

Interesting comments. It made me wonder what they do across the ocean?

Do the pellet speed cops use a chrony? I see post about tuning to the edge of regulation. I wonder how it’s checked.
Normal difference in instruments could get a person in a lot of trouble if shooting close to the limit.

The constables have chronographs on hand to test anyone they feel they need to and they can test with what ever weight projectile they want. Most sub 12 fpe airguns over there are tuned to 10 - 10.5 fpe. to avoid a situation where a constable uses a different projectile or a 2% difference from their equipment that could give higher fpe readings. Only stupid people push the limits of sub 12 fpe across the pond.

 

[Ries]

My chinese chrony differs 20 fps comparing to the FX chrony. I only use them to tune and see what my adjustments are doing.

The chinese one is the one that I use the most, it registers all my shots, the FX one seems to miss some.

 

[Sawney Bean]

At a guess. I would tune to 11.5 fpe and count on the 1/2 lb variation To compensate for off chrono readings and variations in temp.

If you watch some of the airgun reviews from the UK you'll notice that they're usually much more conservative than that, (at least on Youtube videos anyway). What I usually see on those reviews are rifles that are shooting 11 fpe or less. It makes their hunting exploits just that much more impressive when you realize their 12 fpe rifles often aren't even 11 fpe rifles.

 

[LDP]

If you watch some of the airgun reviews from the UK you'll notice that they're usually much more conservative than that, (at least on Youtube videos anyway). What I usually see on those reviews are rifles that are shooting 11 fpe or less. It makes their hunting exploits just that much more impressive when you realize their 12 fpe rifles often aren't even 11 fpe rifles.

Most are tuned to 10 - 10.5 fpe. They also have anti tamper designs on most and most people have a shop tune the airgun. Its much different than here in the states where we have no restrictions and can adjust things without worry of breaking a law.

 

[Sawney Bean]

I only use a chronograph for troubleshooting and ballistics plotting, and I've been loving my FX Pocket. It just works reliably 90+% of the time. Maybe one in every ten or twenty shots it will fail to register but that's so much better than any other chrony I've ever had.

Usually I'll record the average velocity of a shot string with whatever pellet I intend on using, mark that on a piece of tape and stick it to the scope, along with the measured height of the scope relative to the bore. That way I've got a quick and easy way to produce a ballistics chart in the future or to troubleshoot the gun if I start having problems with it.

So far as ballistics charts go, I've been using the Element Ballistics app and I have found their predictions to be very accurate. For guns that I shoot frequently I'll also shoot a few groups at measured distances in order to confirm that the predicted holdovers are actually correct. I don't think you can actually verify the accuracy of the chronograph in this manner however. Every projectile has it's own BC that's determined by it's weight, shape, sectional density, etc..., but that doesn't mean they will fly identically from different guns even if the initial velocities are identical. One rifle might better stabilize that projectile than another resulting in less velocity loss over distance. There's a term for these environmental variations to the ballistic coefficient, but I forget what it is.

 

[Star7]

My only real interest is in relative performance. I use the chrono to trouble shoot or get an idea of shot string consistency. Being a nerd, the Q of just how accurate are these? came up. I have an old Chrony beta, and old Comp. Electronics, a super cheap new Chinese chrono and a Lab Radar. From about 500fps (olympic guns) to 950 fps they are all within about 7fps of each other. That surprised the heck out of me. One thing is that some of these have a very short distance between sensors and I am cautious about trajectory alignment. It would not be hard to induce 5% of more error by angling through the screens.

At the end of the day, relative measurement floats my boat, and I am not about to build a swinging weight trap to check absolute accuracy.

 

[NateChrony]

(full disclosure - i make chronographs)
My devices have (this week) got back from the Australian National Measurements Institute - so I have traceability on those "master" chronographs.
From those master Chronys I calibrate every chronograph I sell, so you know that the readings mine give are accurate, and can be traced to the standards.

Does a NIST traceable chronograph exist?

So yes - there's mine, I believe SKAN also have one that is calibrated.
SKAN claim 99.6% accuracy, thats 4fps @ 1000
I've been able to get at least 99.9% accuracy, thats 1fps @ 1000 (actual results were around 0.3fps)
Prior to that - i had them back to back with the "most expensive radar" & over 20 shots @ 850fps, it was 1fps difference using the average.

I'll be doing a few "calibration" videos on my YT channel shortly - probably the biggest variable: EXACTLY how close are you to the muzzle?
I've been able to measure 3.5fps (from memory) decrease in speed 140mm from the muzzle!

I was chatting with a guy here that makes ballistic materials for police/armed forces, he has a $100k chronograph he gets tested every year. There's things that they dont even account for in their calibration, as its kind of impossible to incorporate.

 

[NateChrony]

(a thread i put up elsewhere)

Some cals to understand what we're working with:
Speed - lets use 1000fps
Sensor distance - 80mm (standard NateChrony)

At 1,000fps it takes 0.000262467 seconds to travel between the sensors.
That's 262.4671916 Microseconds, or millionths of a second.
For every microsecond (millionth of a second), the pellet travels 0.3048 mm.
For the same time period: 0.1mm is 1.25fps

Time Granularity/Resolution
A millionth of a second is tiny! We'll use that - she'll be right?

Keeping the 80mm distance, whats the various time differences to travel between the sensors
around the 1,000fps mark?

FPS - Time
1002 - 261.94
1003 - 261.68
1004 - 261.42
1005 - 261.16

So if you use microseconds, you cannot tell the difference between 1002fps & 1005fps - its all 261 microseconds!


Distance Tolerances, manufacturing, materials
So every microsecond is about 0.3048mm. How good is the assembly process?
What about the actual parts - injection molds typically have a tolerance of 0.127mm & they wear over time.
How much wear? when were they last checked?
I spoke with a guy that has a $100k chronograph that is used to certify ballistic materials. Each year they only check the timing of the circuit - they dont actually check the distances/spacing. Unsure if the device has any wear (hinges/pivots) though.
But this category was HUGE - an easy ~5-10fps can creep in without good assembly & materials.
Think hand built Rolex & not production line processes - we're dealing with those tolerances.

Thermal expansion
Whats the material its make from?
Common plastics can change by 0.1mm per degree over 100mm **(EDIT: I think this was supposed to be 0.01mm)
So 3 degrees temp change will be an error of ~1fps!

Mounting & Vibration
If there is vibration/movement between the muzzle & the chrony - it makes a really big difference.
How rigidly are the two fixed together?
If its mounted on a tripod/bench - how rigid is it? Is there some flex?
(I could detect a difference of ~7-8fps @ 850fps with different mounting techniques)

Alignment
Are you shooting perfectly straight along the sensor axis?
If we take those shoot through chronys, assume a 300mm distance between the sensors.
If you're 10mm off center at the rear sensor, the pellet travelled an extra 0.167mm - thats 1fps!

Sensors
I wont go into this - there's a good amount of tricks around working with this.
The issue is that with an optical type system - the pellet passes through a "beam"
So how much of the beam needs to be blocked before it triggers?
Sensitivities of the underlying components - along with design yields a good amount of variance (~5fps)

Underlying Electronics
This has been really interesting (read "painful"). The exact same electronic components from the same manufacturer, but from a
different batch can perform differently!
There's also how you program the board - take the easy route & use an operating system or use low-level programming?
If you use an operating system there can be a lot of things happening which cause errors that you may not know about impacting timing operations.

Distance from the muzzle
Pellets are always decelerating once they leave the muzzle - so how close is the Chrony from the muzzle?
Have you calibrated the distance from the muzzle?
Using a light 9.5grain 22cal pellet, I can reliably measure a 3.5fps decrease in speed at ~140mm from the muzzle


As with any errors & tolerances (uncertainty) in a system - you need to add them all together.
Ouch!

 

[dgeesaman]

If there’s one thing I’ve learned in metrology it’s that really good numbers are rarely accidental. I’ve seen a LabRadar tick off the same velocity within 1fps 5 shots in a row (1000y BR competitor testing a really good load around 3100fps) so my conclusion is LabRadar is the gold standard for hobby shooters. The Garmin appears to be quite similar in accuracy but their “muzzle” extrapolation formulas aren’t identical. Likewise with my Bulletseeker.

 

[NateChrony]

If there’s one thing I’ve learned in metrology it’s that really good numbers are rarely accidental. I’ve seen a LabRadar tick off the same velocity within 1fps 5 shots in a row (1000y BR competitor testing a really good load around 3100fps) so my conclusion is LabRadar is the gold standard for hobby shooters. The Garmin appears to be quite similar in accuracy but their “muzzle” extrapolation formulas aren’t identical. Likewise with my Bulletseeker.

Radars are also interesting - i *think* doppler radar may be more accurate as velocities increase, larger frequency shift allows more time to count.
But then its decelerating... but you can add maths to correct that.

Ask the manufacturer for testing & results....
I saw a post where Garmin say their devices are all tested & are within 1fps at a known speed (I think 1,000fps)