Range Report Bad Chronograph readings or erratic velocities

TBass

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Apr 3, 2008
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Looking for some advice… I went out early this morning to zero my rifle w/ some new handloads.

* Conditions first thing this AM were: 81F, 47% humidity, Density alt 7255, barometer 25.33.
* My first string of velocities were: 2961, 2972, 2964, 2966, 2969 (with avg velocity of 2966 & std of 5).

Satisfied w/ the loads, I stopped tracking velocities & I then started moving targets out every 100 yards.

100 yds – 0mils / 200 yds - .3mils / 300 yds – 1.0mils /400 yds – 1.7 mils

I left around high noon; however, before leaving I decided to see if the temp (which was now approaching 98F in the sun) had any effect on velocity. I wanted to check this because I have heard from several people that IMR-4350 is very temp sensitive.

I got the following strings: 2609, 2524, 2497, 2538.

Is it safe to assume that because it was so bright out that my Chrony was giving me bad readings? Wouldn’t the heat cause velocities to go up? With such a huge deviation on the last shot string, would I have been able to hit a target at 400 yds & keep the group within 4 inches?
 

Lumpy Grits

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Jan 25, 2005
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Re: Bad Chronograph readings or erratic velocities

Hi, the first thing I do at EACH crono. session is to start with fresh batteries.
Also make sure your crono. is not "seeing" your muzzle blast. That WILL give you some weird numbers for sure.
Respectfully,
LG
 

Bigwheels

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  • Jun 16, 2007
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    Re: Bad Chronograph readings or erratic velocities

    What chrony is it? I have a couple of cheapo Shootin Chronys, & I've found that they don't like direct sun, & I can change the velocity by up to 100 fps by changing the line the bullet travels across the gates. I get my best results by carefully shooting centered across the gates every time. If I'm off to the side even a little it will read low, or high.
     

    USSR

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    Mar 25, 2002
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    Re: Bad Chronograph readings or erratic velocities

    Direct sunlight on the sensors is a no-no. Generally, the chrony will give readings of several hundreds of fps higher in this situation. I always tape a large piece of paper or plastic on top of and between the two diffusers in a bright sunlight situation.

    Don
     

    TBass

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    Apr 3, 2008
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    Re: Bad Chronograph readings or erratic velocities

    I did put something on top of the two diffusers after the erratic reading; however, that did not seem to do anything.

    I think Bigwheels may be on to something... I am not sure that I had it 100% square to the rifle. Additionally, I was having to shoot off the target (considerably lower) to get a reading; thus, I was not aiming at the exact location each time.

    I think I will elect to believe the consistency of the bullet impact 400 yrds, rather than worry about my velocities & SD.
     

    former naval person

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    May 8, 2003
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    Re: Bad Chronograph readings or erratic velocities

    I think sometimes the problem is called, "reading the glint". The screens read the bright reflection rather than the shadow.
     

    858

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    Dec 8, 2004
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    Re: Bad Chronograph readings or erratic velocities

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TBass</div><div class="ubbcode-body">It's a "Beta Chrony" </div></div>

    I have a Beta Chrony and have had a lot of problems with false readings. Whether it's too slow, erratic and slow/fast, too fast, or not reading at all.

    Dawn/dusk and slightly overcast work best, place the chrony as far away from the muzzle as you can, and make sure you are centered in the screens.

    Your other option is to sell your chrony and buy another brand such as PACT or Ohler.
     

    Grump

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    Oct 23, 2008
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    Re: Bad Chronograph readings or erratic velocities

    Mount your Chrono upside-down and let the screens read the reflected light of the diffusers.

    On one funny sunlight day when I forgot the *#$%!!! diffusers, I got great results with the screens sideways getting their light off the side of the white car.

    Either method equals the perfect light of a day that's high overcast.
     

    Greg Langelius *

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    Aug 10, 2001
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    Re: Bad Chronograph readings or erratic velocities

    Sideways would work with my tripod; diffusers, or none with a white background. Upside down would be problematic. IMHO, very good idea, BTW.

    Greg
     

    4Rail_Gunner

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    Jul 3, 2006
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    Re: Bad Chronograph readings or erratic velocities

    I shot yesterday in Direct sunlight and had all kinds of problems.
    but i have a question.

    Would it help to get the diffusers closer to the sensors?
    or does this further hinder the already high sensitivity of being able get a accurate reading.
     

    1911.it

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    Oct 18, 2008
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    Re: Bad Chronograph readings or erratic velocities

    I have a 20 year old Chrony and it works fine most of the time. It gives me the best results when it is ~10' from the muzzle with skyscreens mounted and the path of the round dead center throught the screens. If it ever dies I might replace it with the Competition Electronics ProChrono Digital Chronograph.

    The make-up of your load may have something to do with the erratic readings. For example, once I found the optimum overall cartridge length as measured on the ogive the average deviation came way down. This is a 308 with Varget and 155g Scenars. There are so many variables effecting velocities it takes time to rule things out. There is no way to figure this out without a chronograph.
     

    Grump

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    Oct 23, 2008
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    Re: Bad Chronograph readings or erratic velocities

    Screens closer to the sensors should help.

    I find it useful to NEVER allow direct sunlight on the sensors. A fat piece of masking tape can put a good shadow over it in a pinch.
     

    4Rail_Gunner

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    Jul 3, 2006
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    Re: Bad Chronograph readings or erratic velocities

    I'll try the screens closer next time and get some poster board to put over the top.

    When i say i had bad readings this is the worst 4shot string i had.
    2854,2878,3179,3099
    Shooting a 260 rem with 144gr Lapua 42.7 grains H4350
    way to erratic on the chrono to be true.