Variance between different chronos

[balmo]

I'm a little on the OCD side but is there a significant variance between different band chronos?I have a Caldwell chrono and I'm comfortably at 174pf for my Open Gun. I'm just afraid that it may read different from lets say an official match chrono abd fail to make major.

[Hi-Power Jack]

I don't know that anyone knows, unless they've tried very consistent ammo

over two of each of the chronos out there....     (I'm not saying no one has

ever done this).   

 

But, my Chrony (cheapest chrono there is) does a very nice job vs any Match

chrono (none of which are Chrony's).   

 

And, with 174 PF, you shouldn't have ANY trouble with a match's chrono -

you could run into trouble with temperature or elevation, but you do have

a very comfortable lead with the 174 PF.     

[Steve RA]

My Pro-Chrono and Oehler 35P are within a few fps of each other.  I put the Pro first and Oehler 2nd and shoot thru both at the same time which removes the problem of trying for super equal loads and doing one at a time.

[jwhittin]

Balmo, what matters most in the case of making power factor is the standard deviation. That doesn't vary much between chrono graphs. What's your SD? Add 2 to 3 times your SD to the velocity needed to make PF and you will be fine. 

[balmo]

Here is my recent chrono session. Best SD of 8.8, worst of 27.5. Disregard the 166pf, those were of a different load.

[jwhittin]

This post answers the question about the differences between chronograph. 

 

http://www.appliedballisticsllc.com/Articles/ChronographChapter.pdf

 

I highly recommend reading, especially the section on Trends and Chapter Summary which explains the main takeaway. 

Edited March 16, 2017 by jwhittin

[jwhittin]

Balmo, what's you bullet weight? 

Edited March 16, 2017 by jwhittin

[balmo]

Thanks for the article jwhittin, I'll make sure to read that. Bullet wt is 124gr

[jwhittin]

As I mentioned, for load consistency the SD is what matters most.  As the Applied Ballistics study showed, the SD difference was only 3.6 fps among the typical optical type chronographs. 

 

Keep in mind, at a match, USPSA procedure is to measure bullet velocity (3 samples) and then calculate the PF based on your bullet weight.  Since low estimates can induce failures, I think it’s reasonable to consider the velocity error (negative values only) from the study and the potential impact to PF.  From the velocity error data (Figure 15.17) I get an average of -22.7 fps (average of all units) and -11.9 fps without the outlier.  So it would not unreasonable to see under reporting velocities in the 10 to 20 fps range.   

 

So for a 124 gn bullet you need 1331 fps to make major.  Adding 2 to 3 times your SD (2*10 and then 3*14) means you should be somewhere in the 1351 to 1375 range.  Then you can adjust from there for accuracy, comps, or preferences.  So your data looks good except for columns D and H.

[Steve RA]

Those were the two with different bullets.

[balmo]

My worries are now gone, I chrono'ed my loads using my friend's ProChrono and I got pretty much the same pf.

[Flatland Shooter]

I was told that my Chrony was reading a bit high.  So I shot it.  (Actually it was an accident.)

 

Replaced it with a ProChrono PAL which seems to read a bit slower.

 

Could be a lot of factors but I did up my powder charge on Major loads to be safe.

 

Bill

[Hi-Power Jack]

13 hours ago, Flatland Shooter said:

I was told that my Chrony was reading a bit high.  So I shot it. 

 

I hope your speedometer never "reads a bit high" .... 

[Flatland Shooter]

On 3/19/2017 at 5:38 AM, Hi-Power Jack said:

 

I hope your speedometer never "reads a bit high" .... 

 

Not a problem.  Its a Chevy and I shoot minor.