Chrony Accuracy & Load Development

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Ruger No.1

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In the past I've had reason to question the accuracy of my Chrony readings as they have been so far off suggested manual data ( consistency round to round but off 200 - 300 fps from the manual). Recently I chronied 2 identical loads to ones I had measured earlier and got much different results. A .223 load dropped 300 fps and a .338 WM load dropped 140 fps. Outside temperature was approximately the same the only significant variable was the light. My highest readings came on a day with a solid overcast of clouds and my lower readings on a bright, sunny early morning session. Sunscreens were in place both times.

Any suggestions as to problems, something I'm doing wrong, etc.? Thanks.
 
Was the sun low or overhead? Cloudy or clear? Using diffusers or not?

Sun low in the sky can definitely result in too high (yet "consistent") velocity measurements.
 
The sun was in the same part of the sky both days (9:30 - 10:30 am), I used my sunscreens(diffusers??) both days, and on the clear day my readings were lower not higher as you've suggested they might be.
 
I was getting velocities consistently 300 or so fps higher than was realistic during a couple of range sessions back in February. Aside from the temperature, the only other odd thing was that the sun was lower in the sky and was hitting the photoelectric "slots" on a fairly sharp angle.

I attributed the erroneous results to the light as the chrony had been performing well at ~12-1pm (so temp probably wasn't an issue).

One suggestion is to try your chrono with .22LR ammo. Another forum member suggested that when I was trying to figure out the problem. The point is that .22LR ammo tends to be very consistent in its velocity (it won't be 300 fps out) ;)
 
I once tested my Chrony by shooting through it and an Oehler chronograph back to back. The reading of the downrange unit was a few fps slower, when I reversed the chronographs the downrange one was still a few fps slower. So the bottom line is that they were both reading almost exactly the same, the Chrony just cost a fraction of the price of the Oehler.
 
shotgunjoe said:
Diffusers or not,sunny to cloudy can make that much of a difference in velocity.
Click to expand...

Any idea why that is? Isn't the unit measuring the time from when the first screen has the light interrupted till the second screen does?

I'm just trying to understand exactly how light intensity, or angle, affects the readings. Obviously not enough light can cause the interruption to be missed, causing an error, but why would these variations cause such a differrence in measured speed?
 
I bought one of the first models made like 25yrs ago. I don't think I used it a dozen times in all those years...come to think of it I don't even know why I'm keeping it.:confused: Maybe something to sell in the EE forum at last ! :D
 
python357 said:
I bought one of the first models made like 25yrs ago. I don't think I used it a dozen times in all those years...come to think of it I don't even know why I'm keeping it.:confused: Maybe something to sell in the EE forum at last ! :D
Click to expand...
How Much? :D
 
Cariboo Kid,don't know the mechanics of why,it just is.I have seen it too many times to say it is the individual unit,someone else may be ableto answer this question.
 
cariboo_kid said:
shotgunjoe - I've also heard that how high you shoot in comparison to the unit will affect the recorded velocity as well.
Click to expand...

The reverse is also true, if you shoot much too low it will definitely affect the recorded velocity. ;) :evil: :evil: :evil:

But realistically, keep the sensors shaded so the bullet will have good contrast against the sky or screens. If sun is shining on the sensors then there might not be enough contrast for a good reading. Say one sensor will sense the tip of the bullet and the other sensor (if the sun is shining on it) would read the base of the bullet crossing because it would need more contrast to "trip" the timer. That is how you can get velocity changes.

The same thing can happen if you shoot high, the area that is in contrast is smaller and if the sensors are not identically matched, the readings will be off.

Under even severe conditions the Crony's work quite well. I have measured .177 pellets (1,200 fps) in a semi dim basement and readings were inconsistent until a bit more light was used.
 
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