Chronograph Reading

Stevesdl · Mar 3, 2010

Hi All,
I have purchased a "NEW CHRONY MODEL F-1" and yet to use it. (If I shoot it, I will never tell anyone!

)

I have read the manual and also looked up additional info on chronographs to understand them better. According to my user instructions, the Chrono should be a distance from muzzle to chrono of at least 10 feet for high powered rilfes.

My question is this. If I am to discern muzzle velocity, is not the actual muzzle velocity a little skewed seeing that the chrono is not a few inches from the muzzle?

(I believe I understand the reason why it is at leasat 10 ft - muzzle blast.)

Thank you
Steve

Stevesdl · Mar 3, 2010

My Apologies.

I see someone posted the same question about 20+ minutes earlier today.

The distance reflects minimal difference.

Thank you
Steve

Desert Fox · Mar 3, 2010

Hi' Steve,

The reason why you want it at least 10 feet away from the muzzle is that the shock wave created by the blast will affect the accuracy of the chronograph. Error will also pop up on the screen from time to time, which can be prostrating when you're trying to record a string. The skyscreen on this thing is so sensitive that, it can be affected by the muzzle blast from another shooter shooting near bye. Chrony are notorious for these. I got so fed-up with the errors that I ended up selling mine and bought myself a Pact Professional.

Dufur · Mar 10, 2010

For the money get a pro chrono digital. set it up at 15 ft and don't look back. Larger shooting window too. Mine has worked great for several years now. 100.00 well spent.

Antelope_Sniper · Mar 11, 2010

And if you are shooting a magnum, and it' s too close, you will be picking it up off the ground, and the skyscreen covers will be blown all over the range. You will have a greater variation from shot to shot, then you will from the little differnece you get from setting your chronograph 10 feet out. Heck the early chronographs were 8 to 12 feet long.

Ridge_Runner · Mar 11, 2010

ya get any closer than 10-15' and you get alot of false readings from the shock wave from the muzzle blast.
personaly I set mine at 5 yards, but I do shoot alot of big magnums through mine.
RR

Greg Nolan · Mar 12, 2010

First off , ditto to what was said about distance.
There appears to be a exponential reduction in speed from the time the bullet leaves the muzzle untill it drops at max range. I've used my chrony at 20 feet a few times and the readings have been about a hundred fps slower. The 10 to 12 foot readings are kind of a norm and if you look at the re-loading manuals their readings are taken at about 12 feet. It seems to provide a stable basis for comparison.
By the way. I've found that arc welding rod makes a pretty good replacement for the support rods that come with the chrony when a sudden shift in the earth caused the chrony to veer into a bullet. :roll:
Greg

Ridge_Runner · Mar 12, 2010

I chrony my 7mm AM at 15 ft, I average 3566 fps.
so I enter that into my program, set the starting range at 5 yards, I keep bumping the MV up until my 5 yard velocity is 3566 fps, my actual mv is 3575 fps, so I lose 8fps that first 5 yards.
RR