CHrono Woes

[FRANK21]

I am a bit confused with my new PRO Chonograph Digital. It seems to read velocitys approx 100fps slower than my Chrony F-1. (That met an untimely demise)
Here are a few velocitys that were chronred on the F-1 and the Pro Chrono.

308win- 26"bbl, 45.5gr Varget, 175VLD
F-1= 2750, PC= 2650

308win- 26"bbl, 45gr Varget, 175smk
F1=2725, PC= 2625

2-223Rem- 26"bbls, 25.5gr Benchmark, 55gr BK
F-1= 3350, PC=3250

7mmRemMag- 28"bbl, 63gr RL22, 180 VLD
F-1=2975, PC=2870

I never chronoed the load below on the F1.
300wsm- 29"bbl, 68.5 RL19, 190VLD
PC= 3000fps


I then tested a friends 308win:
24" bbl, 45gr varget, 175smk
PC=2560, I figured it should be 2650-2700.

I used the 7mmRemMag and the 308win @ 800yrds 2weeks ago and they both supported ballistic charts that I made with the data from the F-1.

Anyone had a problem like this before?
Which one should I believe? Im guessing the F-1.
Any help would be greatly appreciated.

 

[sniper2]

I have had 3 of the Chronys got rid of the 2 that gave the most vel kept the conservative one it works well with my ballistics programs. I would suggest going with the one that worked with your ball. program ,the pro Chrono would probably be more trust worthy although I haven't seen a devise to calibrate any of them with... /ubbthreads/images/graemlins/wink.gif

 

[rotorhead]

Buy a Oehler

 

[lazylabs]

Oehler is not an option anymore, thier web page says they are no longer selling personel chrono's.

 

[Mikecr]

If you know someone with an Oehler, see if you can borrow it. Then calibrate yours by adjusting screen spacing.
It don't take much adjustment to be off that much.

 

[rotorhead]

[ QUOTE ]
Oehler is not an option anymore, thier web page says they are no longer selling personel chrono's.

[/ QUOTE ]
Well isn't that a crappy deal.

 

[Guest]

[ QUOTE ]
Oehler, ... it. Then calibrate yours by adjusting screen spacing.
It don't take much adjustment to be off that much.

[/ QUOTE ]

Great idea. I'll try to talk my local club into buying one. I have two Chronys and they are very consistent. I assumed that meant they were accurate but perhaps they are just off by the same factor /ubbthreads/images/graemlins/smile.gif

 

[CatShooter]

I have a problem/question...

I have two chronographs.

They are both top of the line, and both are accepted as "standards" in the shooting field.

... and they are 150fps "Different", and I need to know real velocity, not just relitive velocities between loads.

How can one determine which is on (or if they are both off).

Whatever the solution is, it must be tracable to an accurate standard... you can't say "use 22 rimfire ammo" cuz it's not an accurate standard.

Any thoughts?? This is not a not a mental trap, it's a real question/problem...

.

 

[Mikecr]

I don't see how an optical chrono could be calibrated. I've been thinkin about building accoustic screens(using microphones) for my Oehler. This could be calibrated with a audio frequency standard(like 1khz).
It could trigger off the bullet's shock wave, rather than shadow. Like that used in the Oehler43 system.

It would help if I had a schematic or atleast a technical description of my chrono operation though.

 

[CatShooter]

[ QUOTE ]
I don't see how an optical chrono could be calibrated. I

[/ QUOTE ]

You need a known source of speed, then you adjust the spacing of the traps so the chrono matches the known sourse. I just can't figure a way to do it.