GR&R for chronys?

[Soloshot]

Anyone know of a study to check the chrony (fps) variation between brands and within same models? Curious after several equipment checks showed 2-3% off results from home tune. Does not sound like a big deal when limit is 20fpe but can get close for 12 fpe. So in case where your home chrony tune is lets say 905 fps for 10.3gr pellets and at a match the gun checks 880fps, that is 25 fps off. Now when tuning a springer at 13 fpe, do you factor in discrepancy percentage (-2.7%) or the absolute value (-25 fps) assuning the match chrony as standard?

 

[corny]

Right now I own a pro crony, Caldwell, and fx 

none of them give me the same reading. Eveb shooting though all three at the same time…most time I see a spread of 25-30fps 

 

[Soloshot]

Right now I own a pro crony, Caldwell, and fx 

none of them give me the same reading. Eveb shooting though all three at the same time…most time I see a spread of 25-30fps 

Good so I am not being paranoid! Work in an industry where repeatability has to be in PPM. So the 3 percent variance caught me off guard. So now the only question remains, for error correction (different rifles/different velocities) do you go by +-30fps or +-3%? (not going Six Sigma).

 

[2D1C]

I have a Caldwell and an FX, neither read the same. Bigragu and I tested his chronies and mine together and there was up to 50FPS difference. Dunno which one is correct

 

[Soloshot]

Right now I own a pro crony, Caldwell, and fx 

none of them give me the same reading. Eveb shooting though all three at the same time…most time I see a spread of 25-30fps 

I have a Caldwell and an FX, neither read the same. Bigragu and I tested his chronies and mine together and there was up to 50FPS difference. Dunno which one is correct

Is there a pattern between the Caldwell and the FX in your cases? Does the Caldwell read higher or lower than the FX?

 

[MikeVV]

Solo -

3%, HAA, who are you kidding ? 

Some brands "claim" 3% to 10% on "repeatability" and down to .01% on "accuracy". I seriously doubt it.

Like you, spending my most all of my working life (Aerospace Industry) expecting to see (realistically !) 3% to 5% in both accuracy AND repeatability. And with the hope of .5% to 2.0% in accuracy AND repeatability, but this ISN'T likely.

And as you say..."accuracy" is a MUCH secondary piece of information to the "repeatability". I'd MUCH rather see an "accuracy" reading of feet per second reading of 850fps, ACTUALLY be 875fps, but in reality I MUCH rather see the "repeatability" of no more that about 2% of the tools scale reading.

Tools reading less than +/-2% accuracy and or repeatability IN REALITY, would cost MUCH more than most any of us could afford. A +/-3% tool is expensive enough.

This is all much like people using a normal dial indicator, and expecting to read "EXACTLY" to three decimal points. Sorry, it ain't gonna happen...accurately. In the manufacturing industry, it's pretty much a "rule of thumb", if you want to measure somewhat "accurately" to two decimal...places, your tool NEEDS to measure to three decimal places. And if you want to measure, somewhat...accurately to three decimal places, your tool needs to read to...four decimal places...and so on.

Oh yeah...DO NOT depend on the first 10%, or last 10% of your torque wrench being accurate ! Even the tools manufacturer will tell you this fact ! and this is for a "quality" wrench .

Just the way life is in the measurement world.

Mike

 

[buckyusn]

Giles (Airgun Gear Show) did a video about the FX Pocket Chronograph where he compared the results of different chronographs. From the perspective of "which one is most accurate or correct" it really seems to be up to the user. So long as the box is consistent . If you are concerned about not being under an FPE limit (e.g. 12 FPE) I guess that you might want to err on the conservative side (-30fps or -3%). Another option would be to use the same brand and version of chronograph as the enforcement agency that would check you for violation.



Apologies if I missed the question. Merry Christmas!



https://www.youtube.com/watch?v=wM53F1naSJE

 

[Soloshot]

Thanks buckusn, exactly what I was looking for. The giles setups were reporting within 1% of each other so pretty tight. I use a Caldwell for tuning and so far it has compared higher than references so safe.

One unanswered question is the correction factor. For example if my Caldwell is reading 30fps higher at 1000fps, would it also read 30 fps high at 500 fps or will it be a percent value, in that case it will read 15 fps high at 500. Just keeping mind busy while watching "It's a Wonderful Life"

Merry Christmas to you too and thanks for the video.

 

[corny]

Right now I own a pro crony, Caldwell, and fx 

none of them give me the same reading. Eveb shooting though all three at the same time…most time I see a spread of 25-30fps 

I have a Caldwell and an FX, neither read the same. Bigragu and I tested his chronies and mine together and there was up to 50FPS difference. Dunno which one is correct

Is there a pattern between the Caldwell and the FX in your cases? Does the Caldwell read higher or lower than the FX?

From what I’ve seen it’s higher. 


I actually had it replaced one time. But it’s still reading higher on average than the other two. Possibly thought…it’s the only one that’s giving me the correct reading 


the pro crony appears to be the most stable…and the fx just has to many random readings 

 

[corny]

Solo -

3%, HAA, who are you kidding ? 

Some brands "claim" 3% to 10% on "repeatability" and down to .01% on "accuracy". I seriously doubt it.

Like you, spending my most all of my working life (Aerospace Industry) expecting to see (realistically !) 3% to 5% in both accuracy AND repeatability. And with the hope of .5% to 2.0% in accuracy AND repeatability, but this ISN'T likely.

And as you say..."accuracy" is a MUCH secondary piece of information to the "repeatability". I'd MUCH rather see an "accuracy" reading of feet per second reading of 850fps, ACTUALLY be 875fps, but in reality I MUCH rather see the "repeatability" of no more that about 2% of the tools scale reading.

Tools reading less than +/-2% accuracy and or repeatability IN REALITY, would cost MUCH more than most any of us could afford. A +/-3% tool is expensive enough.

This is all much like people using a normal dial indicator, and expecting to read "EXACTLY" to three decimal points. Sorry, it ain't gonna happen...accurately. In the manufacturing industry, it's pretty much a "rule of thumb", if you want to measure somewhat "accurately" to two decimal...places, your tool NEEDS to measure to three decimal places. And if you want to measure, somewhat...accurately to three decimal places, your tool needs to read to...four decimal places...and so on.

Oh yeah...DO NOT depend on the first 10%, or last 10% of your torque wrench being accurate ! Even the tools manufacturer will tell you this fact ! and this is for a "quality" wrench .

Just the way life is in the measurement world.

Mike

Absolute…and even with the right tools. Often two different ppl with get two different readings. 

 

[corny]

Giles (Airgun Gear Show) did a video about the FX Pocket Chronograph where he compared the results of different chronographs. From the perspective of "which one is most accurate or correct" it really seems to be up to the user. So long as the box is consistent . If you are concerned about not being under an FPE limit (e.g. 12 FPE) I guess that you might want to err on the conservative side (-30fps or -3%). Another option would be to use the same brand and version of chronograph as the enforcement agency that would check you for violation.



Apologies if I missed the question. Merry Christmas!





https://www.youtube.com/watch?v=wM53F1naSJE

I find the fx is a lot more fuzzy as a whole. to me it just brings another layer of unnecessary complications to the table. On average, when I shoot through my three crony at one time, the fx will result in the highest ES consistency. 

 

[cmatera]

I had an Oehler 35P. setup was a PIA, but in my 25 years of shooting, I trusted it the most.

 

[bigHUN]

Over past 20 years in archery I had all the possible variations of chrony's sometimes 2-3 of them in same time. Finally I just gave up looking for the best.

Don't go further, just visit your HomeDepot or any of your home hardware stores, and sandwich together couple "i-beam" levels. How many you will see two bubbles match? Very entertaining you shall try next time there. Finally you will just pick one and call it a day.  

 

[corny]

Long term…I plan on getting something like the lab radar.

being within 30fps isn’t good enough. Most certainly not for $100-$200 product.

 

[corny]

Over past 20 years in archery I had all the possible variations of chrony's sometimes 2-3 of them in same time. Finally I just gave up looking for the best.

Don't go further, just visit your HomeDepot or any of your home hardware stores, and sandwich together couple "i-beam" levels. How many you will see two bubbles match? Very entertaining you shall try next time there. Finally you will just pick one and call it a day.

All depends what your aim is. One of the best ways to solve problems is to remove factors from the equation. 
Accurate tools that can be trusted can accomplish that. 

I’m the machine world…we use high tolerance machine levels, they are calibrated and repeat. 

 

[JungleShooter]

Being within 30fps isn’t good enough. Most certainly not for a $100-$200 product.

So, let's say I measure a JSB dome's BC with two chronos.

True MV = 939fps

True V @50y = 750fps

True BC = 0.0301 ➔ At 100y a 15.89gr dome in a 5mph crosswind drifts 7.3".

BUT the "True Truth" is not known because of our chrono error: we get some funky measurement variations:



Chrono 1 fluctuates just half of that vile 30fps UP, instead of showing 939 it shows 953fps.

Chrono 2 fluctuates just half of the 30fps DOWN, instead of showing 750 it shows 735fps.

BC now only shows at 0.0260 —— and instead of the 7.3" correct wind drift we would calculate 8.5" wind drift — a whole 1.2" more drift — because of the chrono error of 15fps.

Now, chrono 1 is dead on! showing 939fps.

Chrono 2 fluctuates the vile 30fps DOWN, instead of showing 750 it shows 720fps.

BC now only shows at 0.0249 —— that's even worse that the previous example....

Of course, my hope would be that if I have enough measurement data points, the fluctuations will even each other out....

For that I'd have to compare the chronos side by side and see if one has a tendency to always read higher or lower than the other chrono.



And if they do — then what do I do....?!?

Matthias