Real world trajectory data

Forums General Airgunning Real world trajectory data

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    fishinwrench
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    After a lengthy chronograph session, or more like 5 of them, the trajectory data on chairgun and strelock wasn’t accurate, so here’s what I did…… 
    I carefully shot a 5 shot group at 30yds and another at 40yds, then accurately measured the drop.   I then pulled up Chairgun, entered my projectile and scope height data and then altered the FPS until the drop between 30 and 40 yds. matched the ACTUAL drop measurement.  
    Ureaka!  My trajectory chart is now spot on at all ranges, and I mean DEAD ON from 15 to 75 yards (and probably beyond, but 75 is as far as I will ever shoot).  

    Now, whether chronographs (even the very good ones) are bullshit, or the B.C. is the reason……it doesn’t matter.   Who needs a damn chronograph if the numbers are unreliable ?    The real world FPS of my set-up is 86 FPS different than what the best chronograph on the market says it is.  

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    Oregun
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    Very interesting!
    Was the 86fps high or low?  What are you shooting (gun & cal)?

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    1BadDart
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    Have you calculated you actual BC compared to Chaigun?

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    GLPalinkas
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    Hard Air Magazine did a ballistic coefficient chart a few months ago and published the result. I am curious how your results compared.

    Here is the link:

    Ballistic Coefficients

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    oldspook
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    “fishinwrench”Now, whether chronographs (even the very good ones) are bullshit, or the B.C. is the reason……it doesn’t matter.   Who needs a damn chronograph if the numbers are unreliable ?    The real world FPS of my set-up is 86 FPS different than what the best chronograph on the market says it is.  
     

    
This happens because the BC of the pellet changes with  a whole host of factors.  BC is velocity dependent, meaning that it changes as the pellet looses velocity.  BC is changed by anything which changes the shape of the pellet,  so number of lands and grooves, actual bore diameter, for example.  BC changes when air density changes, thinner air (higher altitude) better BC, thicker air (lower altitude) worse BC.  Humidity is a factor… etc.. yada yada.   You can’t get exact results by using the BC numbers that Chairgun provides.  They are there to give you a starting point.  The method you have just used is quite valid and you could compute your true “average” BC from the information you have now collected, or let Chairgun do it for you.  ;)  Good thinking.

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    2D1C
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    I found the same thing. The shoot card was good to ninety yards then was off 1 click (low) I had to adjust it down to 835 fpe (.25 Airwolf) which is about 20 fps below my average.
    Be interesting to see how it works when my crown gets here.

     

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    fishinwrench
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    “Oregun”Very interesting!
    Was the 86fps high or low?  What are you shooting (gun & cal)?


    My real world velocity is lower than the high dollar chrony showed.   Of all the chrony testing I have done, believe it or not, that stupid Chrono–connect app on my phone is the closest to my real world calculations (which according to chairgun and my POI at different ranges, is 100% balls-on accurate).  

    I’ve been at this since 10:am this morning.  Three different guns /w 4 different pellets.  Results are the same on all.   I’m happy as can be.  I don’t give 2 shits what the true BC is, nor do I care what my TRUE velocity is , as long as I can hit dead on at all known ranges consistently.   To me that’s all that matters.  And this backwards method flat works.   

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    fishinwrench
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    “GLPalinkas”Hard Air Magazine did a ballistic coefficient chart a few months ago and published the result. I am curious how your results compared.
    Here is the link:
    https://hardairmagazine.com/ballistic-coefficients/


    Those BC values are no different than Chairgun’s on the pellets I am using.

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    SDellinger
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    This is my drop chart. I manipulate Chairgun untill it matches. I change the scope power instead of velocity or bc. It’s a long complicated story how it works for me but it works. Have fun, Scott

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    fishinwrench
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    Double post, sorry

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    Diamondback
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    Saw some Si Pittaway videos about doing this with Chairgun:

    The Near & Far Calibration Method

    Secrets of the 3 shot calibration with VerminHuntersTV’s own Si Pittaway (part 1 of 2)

    Secrets of the 3 shot calibration with VerminHuntersTV’s own Si Pittaway (part 2 of 2)

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    markT
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    Completely agree with you Fishinwrench.. Apps are just apps. What you gun shoots are the facts.. the only way to know is to shoot your rifle and mark / paint the elevation adjustments on your scope. 

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    Oregun
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    I had a similar experience this past weekend.  I haven’t shot in about 2 months and was sighted in for my backyard at 17ds.  It was dead nuts on at various ranges using chairgun the last time I shot at 50, 70, 90. 

    Last Saturday, my buddy, Dave and I headed out to the coast range for a day of shooting.  We set targets at 50, 62 & 85 yrds.  I shot a few strings at 50 without making any adjustments.  I was hitting high with nice groups,  I then made my adjustment according to the App.  very slight shift, not what I was expecting as it was still high and tight.  After 30 or 40 minutes of hair pulling, I shot at the 62 yrd target.  It was close to target.  Just a couple clicks, I was spot on.  

    Long story short, I used holdover at 85 and 50 the rest of the day.  The variables or differences from that day include, elevation (2000ft), crystal clear, no humidity, temps in the 50’s. (perfect conditions!).  My theory was my gun was shooting hot 
    I’m mystified…

    • This reply was modified 3 months ago by Oregun.
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    fishinwrench
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    If I could just own a rifle/scope combo that would hold zero for more than a couple days I would be the happiest man in town.

    Does no good to zero my turrets because my zero will be 5 minutes away tomorrow. 😖

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    Alejandroo
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    “fishinwrench”

    “Oregun”Very interesting!
    Was the 86fps high or low?  What are you shooting (gun & cal)?


    My real world velocity is lower than the high dollar chrony showed.   Of all the chrony testing I have done, believe it or not, that stupid Chrono–connect app on my phone is the closest to my real world calculations (which according to chairgun and my POI at different ranges, is 100% balls-on accurate).  
    I’ve been at this since 10:am this morning.  Three different guns /w 4 different pellets.  Results are the same on all.   I’m happy as can be.  I don’t give 2 shits what the true BC is, nor do I care what my TRUE velocity is , as long as I can hit dead on at all known ranges consistently.   To me that’s all that matters.  And this backwards method flat works.   

    
Have you tried with Strelok Pro doing the same thing that with Chairgun but after firing an making test for drop at longer ranges you go to the “truing” option inside the app and with all that the app makes somekind of cross-reference between your theoretical chart values (given by the app at the beginning) and the real world results to give you the best possible outcome.
    I remember that Matt Dubber has a youtube video on the process in his channel, in that episode his shooting a .260 REM to about 700 meters, check it out it might help or not……at least you can compare it with your method and let us all know, thanks!

    Alejandro

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    fishinwrench
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    Alejandro, To be honest I hate dicking with apps, programs, and computers in general.  
    I have stumbled upon a system (however crude) that truly works, and I am done experimenting and tinkering.   😎

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    Oregun
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    “fishinwrench”

     

    
Great results…  I’ll follow suit and give it a go!

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    John_in_Ma
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    “Oregun”I had a similar experience this past weekend.  I haven’t shot in about 2 months and was sighted in for my backyard at 17ds.  It was dead nuts on at various ranges using chairgun the last time I shot at 50, 70, 90. 
    Last Saturday, my buddy, Dave and I headed out to the coast range for a day of shooting.  We set targets at 50, 62 & 85 yrds.  I shot a few strings at 50 without making any adjustments.  I was hitting high with nice groups,  I then made my adjustment according to the App.  very slight shift, not what I was expecting as it was still high and tight.  After 30 or 40 minutes of hair pulling, I shot at the 62 yrd target.  It was close to target.  Just a couple clicks, I was spot on.  
    Long story short, I used holdover at 85 and 50 the rest of the day.  The variables or differences from that day include, elevation (2000ft), crystal clear, no humidity, temps in the 50’s. (perfect conditions!).  My theory was my gun was shooting hot 
    I’m mystified…

    
I feel you aren’t giving mother nature her due in it’s interaction with your ballistics. You say it was in the 50’s. Shooting from shade into sunlight over melting snow means there is some humidity in the air as the snow is evaporating from the temperature, and even more so from the sun. This will create differentiating thermals affecting your projectiles flight path. I’m honestly surprised you didn’t catch a mirage in your scope at the point where the shade and sun meet. That can also cause what appears to be a shift in the optics. Of course your gun could have been shooting hot, or gotten knocked or bumped to cause a shift but I think given your location and the weather/range conditions there’s enough mother nature there to mess with ya.

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    Oregun
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    Good catch, John. 

    I was thrown off as my shooting bud was on target from the start and it took me 30 minutes or so to get going.  Typically, I rely on the app.  Something was out of whack. 

     

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    BEN342R
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    Based on this thread, I can see now why Ted Bier likes his MTC scopes so much.  Just 
    make a range tape for the top turret and your done.  I pest mostly at home, and have all the ranges mapped out in my head.  I think I will try a Viper pro since I am in the market for a new scope, and I don’t want or have time to screw around with calculations when I need to take shots quickly.  👍🏿

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