Chronograph Accuracy

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DesertRatR

New member
I couldn't find any other forum where this fits so here it is.

I have a Chrony Beta. I measured some new 45 ACP loads today and found the numbers hard to believe. The sky was overcast with no direct sun at all. That makes me wonder if the unit is working properly in what is effectively low light. The manual says nothing about low light conditions. No error codes were reported. But perhaps the signal-to-noise ratio is a bit lower than in bright sunlight.

What makes me suspect the data is the average speed was significantly higher than what the loading manual says it should be for the load. I am using a bullet in the manual (not a "similar to"). Both the extreme spread and standard deviation were much greater than I've ever seen. The recoil seemed normal, not hot.

I calibrate my scale with every use and also check it with check weights. I always discard the first 25 powder drops before starting to load. I've measured powder drops to be very accurate, over a range of loads, with standard deviations of no more than 0.1 gr and and +/- tolerance also no greater than 0.2 gr, usually closer to +/- 0.1. I am confident the load is what I expected.

Obviously the thing to do is reload and repeat the test in bright sunlight. However, I was wondering if anyone has experience using a Chrony in low light conditions. I assume calibration is not possible.
 
Chronographs are not the same kind of precision instrument as scales and volumetric measures.

Scales and measures work with physical solids. Chronographs measure light (shadow) and sunlight IS rather variable.

I have seen a Chrony run fine at noon, reading everything, and by late afternoon getting erratic or no reading on .22-250 bullets while reading .45 cal slugs just fine until there wasn't enough light for it to read, at all.

best thing I can say is don't take any given set of readings outside the normal as gospel, consider them suspect, unless they prove repeatable in ALL conditions.

Don't know anything about calibrating a chronograph, sorry.
 
In general, the best light condition for optical screen chronographs is "cloudy bright". It's direct, clear sunlight that sometimes confuses them, especially if the angle of the sun is such that it shines directly on the sensors. In my former line of work, a key principle was, "Believe your indicators." Look to your loads first. One chrono error that would cause the behavior you describe is having the screens too close to the muzzle. But that's usually too slow due to tripping the front sensor prematurely.

PS: The classic chrono check is to run a standard velocity, or better, match .22 LR through. These are very consistent.
 
Chronographs can be finicky and bright but cloudy conditions seem the best, few shadows.
I have a Shooting Chrony Beta Master sitting on a shelf in my garage, which is the only thing it's good for. Most of the time it gave bizarre readings or errors, once in a while a reading would make sense but it's so unreliable I never trusted it.
I now use a Competition Electronics ProChrono. It has been very good, consistent and rarely fails to read.
 
I have found that I get fewer missed/erratic shots from my chrono if I use a white sunshade above it. A piece of dollar store foam board cut to size and attached with a few pieces of stick on velcro from a hardware store works wonders for dropped shots and erratic readings.

I shoot a lot in early mornings and the sun filtering through the leaves sometimes confused my chrono if I shoot from the left side of the range before the sun gets above the trees
 
This is a pretty good read on chronographs. What the article does is make suggestions on how to get reliable readings from a chronograph and some things which can contribute to errors.

With the exception of newer designs like the Lab RADAR all chronographs operate about the same. The heart of the chronograph is a clock circuit (oscillator circuit) which generates pulses of a known frequency. When a bullet crosses a first sky screen (sensor) it opens a gate allowing clock pulses to be counted. When the bullet crosses the second sky screen it closes the gate. With a known distance between the start and stop sky screens the velocity of the projectile can be calculated. A chronograph can be checked or calibrated but the needed instrumentation is not available to the average shooter. The Velocity = Distance / Time as the article points out. The screens provide a start and stop pulse opening and closing a gate. The process all begins with having good screens to generate the start and stop pulses. To simulate the pulses would require instrumentation not available to the end user in most cases. Additionally the internal clock (oscillator) is subject to variables like heat and cold as well as humidity. The better the clock the more stable it will be and the clock stability is a big player. The average shooting chronograph uses rather inexpensive clock circuits which have some drift. The gate triggering is also important.

Without getting into too much detail trying to check the accuracy of a chronograph would not be a simple process for the average end user. As 44 AMP mentions, scales and volume measure devices are much easier to test than a chronograph.

Ron
 
What makes me suspect the data is the average speed was significantly higher than what the loading manual says it should be for the load.
Click to expand...
Different test gun/barrel, barrel length, temperature, altitude, powder lot, bullet, crimp, neck tension, dies, seating depth, case brand, etc. all make a difference. I was suspecting my chronograph was off, and a fellow shooter brought his out (different brand even). We set them up back to back, and the difference in velocity was only a few fps. I was reading higher velocities than I thought I should be getting for the barrel length I was using. I even got a set of check weights to verify that my powder scale was reading correctly. Everything checked out. So, I just accepted the the fact my chrono was 'ok' working at 5000 ASL, and went on testing loads. Oh, I have an F1.
 
DesertRatR wrote:
I was wondering if anyone has experience using a Chrony in low light conditions.
Click to expand...

Yes.

First check that the plastic diffusers on your screen have not deteriorated. If they have, replace them (or make your own).

Second, if ambient light is not sufficient, ShootingChrony sells a set of illuminated
http://shootingchrony.com/products_ACCESSORIES.htm for about $60 that will ensure the sensors have plenty of light to "see" the bullet pass.

Third, remember the ShootingChrony device (regardless of what additional features it might have, is simply a pair of light sensors connected to an electronic timer as Reloadron already explained. The oscillator is sensitive to the applied voltage so make sure the battery powering the unit is fresh.

Finally, the ShootingChrony unit has no provision for user calibration. That means if it's oscillator registers 38 microseconds when the "true" time was 35 mircoseconds, the velocity reading will be inaccurate. But, that shouldn't be a problem since the ShootingChrony is a piece of range equipment, not laboratory equipment and even if all the velocity readings are off by a few percent, the unit is still sufficient to tell you what you really need to know; whether your rounds are in a velocity "neighborhood" and whether or not you have achieved round-to-round consistency.
 
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