Differences in Chronograph Readings

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by D.Camilleri, Apr 14, 2013.

  1. D.Camilleri

    D.Camilleri Well-Known Member

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    Went to the range yesterday to work on my drop charts with 215 Bergers in my 300rum. I set up both of my chronographs two feet apart about 10 feet in front of the muzzle. Older chronograph is a pro chrono, and the newer one bought last year is a Chrony F-1.

    First shot showed 3075 through the Pro Chrono and 3163 through the Chrony. Then I put the 338rum in front of the chronographs and recorded 2780 through the Pro Chrono and 2870 through the Chrony.

    My 338 rum loads have been proven out to 1250 and the velocity comes out to 2830 with the 300 gr Berger OTM Hybrid gen II.

    With the numbers entered into exbal on my PDA, using 3025 as the velocity for the 300 rum with the 215 berger I am hitting a consistant 3 inches low at 690 yards. I need an additonal .25 moa up to hit the mark and to get there, I think my calculated velocity needs to go down to 3000.

    Anyone else out there with Chrony's have them showing fast like this?
     
  2. Cornfield Flats

    Cornfield Flats Active Member

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    I'm glad to see someone post this subject. I was going to a long time ago but just didn't want to get into it.

    My results with these two brand name chronographs has been almost identical. I have tried three different Chronys, two Pro Chronos and two Oehler 35 Ps. In every case, the ProChrono read very close to the Oehler; within single digits. The Chrony would read up to 110 fps faster depending on the muzzle velocity of the load. It didn't matter which chronograph was in front. It seems like a percentage difference. The higher the muzzle velocity the more the difference.

    I suppose one could argue the Chrony is right and the others are wrong but that's not likely. I develop my drop charts using data from the Oehler or Pro Crono and everything seems to work out correctly.

    Thank you for posting this.
     

  3. cowboy

    cowboy Well-Known Member

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    Been there - done that. My chrony read high compared to back to back with other chronographs as well as actual field testing. Dang near put a bullet through it one day. After settling down after a few days I called chrony. Sent it in and they re-calibrated it.
    By the way - they test/check/calibrate with a pellet rifle.
    Mine read consistently 35 fps high at 2850 fps.
    It is caused by the two reading eyes (little black boxes) being too close together or too far apart.
     
  4. D.Camilleri

    D.Camilleri Well-Known Member

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    The reason I bought the Chrony was because I have a friend who has a Chrony and he was recording faster velocities than I was, plus I have a loose wire on the pro chrono and sometimes it doesn't want to turn on. I have another friend that just bought a new chrony and he is recording some abnormally fast velocities from the 300 wby with 215 Bergers. Since he is new to long range shooting, I don't want him to get all frustrated when his drops don't match his G-7 range finder. In the past, it was always easy to blame the bullet maker's B.C. as being wrong to validate the velocity that was read with the chronograph. Now I have come to the conclusion that what the chronograph says really doesn't matter, get the velocity to match the drops and go with it. It just annoys me to buy a piece of equipment and not have it even be close to what it should be. I think the chrony is going on ebay for sale and I am going to keep my eyes open for an ohler. It is kind of hard to strive for a gun that shoots sub 1/2 moa only to have a chronograph that is the equivilent of shooting a 3 inch moa.
     
  5. CliffM

    CliffM Well-Known Member

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    Do you think it is possible to not have it opened all the way and have the eyes looking a bit inward (that would be crosseyed). I have discovered mine lying from time to time and this makes me wonder if not setting it up the same every time could be it.
    Cliff
     
  6. Greyfox

    Greyfox Well-Known Member

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    I also have these there plus a Superchrono Acoustic. The Chrony reads typically 75-100 FPS faster then the others which ate close given it an overcast day. This occurs with both my 300WM and 6.5x284.
     
  7. cowboy

    cowboy Well-Known Member

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    All I can tell you is that setup with the Chrony's is critical. I like to run 2 chronographs back to back to give me a warm and fuzzy feeling.

    With the one F-1 that I have I can only tell you what I do to not get frustrated.

    1) I set up the F-1 at a minimum of 15 ft. from the muzzle of rifle - and I measure this with a tape measure, make note of it, and after a session I plug into ballisitic calculator to get true muzzle velocity. At 2800+ it usually adds about 7 fps to actual reading on chrony with 168 Berger VLD's on a .284 bullet. With a heavy boomer with brake I set up chrony at 20 ft. from muzzle..

    2) I bought an old style folding 3 legged surveyors tripod at a pawn shop (20 bucks) that is sturdy as all get out and adapted a bolt/nut to tripod head to fit my chrony. After setting up chrony the correct distance I want, I level it both ways with a 6" torpedo level. I think since I started doing this it has made a world of difference in that I can't remember the last ERR reading that I got.

    Having a very solid base (tripod), keeping it far enough away to prevent any muzzle blast having an effect, and getting it perfectly level has now allowed my cheap chrony to run right with some of the more expensive units.

    I would encourage you to send your chrony back to get re-calibrated if it is truly reading high/low. They are good people to work with and it only cost me postage one way. Keep in mind that these units are acceptable if they read within + or - 3%. For me that is not acceptable as plus or minus 3% of 3000 fps is 90 fps at it's worse senario.
     
  8. CliffM

    CliffM Well-Known Member

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    cowboy
    Thanks, looks like I need to pay attention to the details quite a bit better. I do get ERR often.
    I usually just stretch out the cord, set the tripod down, line up on the target and go to shooting. It might be like getting a new one if I am a bit more careful about things.
    Cliff
     
  9. cowboy

    cowboy Well-Known Member

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    Hope things go well for you. Keep them moose safe down your way as I'm sure G&F have a tag with my name on it this year and I've got a couple ponies that haven't smelled moose blood yet :)
     
  10. MontanaRifleman

    MontanaRifleman Well-Known Member

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    A little late, but I'll mention I have the ProChrono and Shooting Chrony Alpha.

    Started with the ProChrono about 15 yrs ago and got the Chrony A a couple years ago. I've set them up back to back a few times and I got variations anywhere from 5fps to about 70 fps and it and usually an inconstant variation.

    The ProChrono seemed to give more accurate and consistent readouts based on published loads and factory published load velocities. The ProChrono usually works very well on overcast days. On Sunny days it will give more inconsistent readings including occasionally as much as 200 fps off, both high and low.

    One day last week, It was reading about 3350 fps for a RUM load I was using, during the afternoon in the sun. A few hours later, i returned and the shadow of the overhead shelter moved out over the chrono and the readings went up to 3400 for the same load, just like that.

    This is why I put limited trust in chronograph readings. I think they are good for ball park info, but that's about it.
     
  11. D.Camilleri

    D.Camilleri Well-Known Member

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    What I see as the problem with faulty chronograph readings is there are more and more people learning to shoot long range and while having a chronograph is a good tool, people need to understand that you must shoot your load at distance and prove your velocity and not just rely on what the chronograph tells you. It really helps to have some better numbers for accurate B.C.s available lately because that takes away another unknown. Information out is only as good as information in.