6.5 Creedmoor seems to fast?

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by backcountryguide, Jul 5, 2013.

  1. backcountryguide

    backcountryguide Well-Known Member

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    Guys I finally got some good conditions and went to the range to true up the drop chart. I am using shooter on my iphone and a Kestral to input my data. The chrono gives me 2975fps from 43.5gr of H4350 and a 140VLD. I input my station pressure at 23.4 with a temp in the low 80's. I dial in .2 mills for spin drift and .2 more for the wind. First round at 1009 yards is about 3/4 mill high but dead center for wind. I dial down and plant the second one dead ceater on the plate. Four more and we head up to check the group. A very nice 5in group with almost no vertical. I input into shooter what I dialed to get the group and it spits out my velocity is 3070fps. I say out loud that that cant be. We then hang steel at 500, 700, 900, and repaint the 1230 yard target. I start shooting using the new data and it is spot on all the way out with a 8in group on the 1230 target. Our range sits at 6500ft but I only input station pressure into shooter since the kestrel gives me the true pressure. The rifle has a 28in Bartlein on it but this seems to fast to me. Any thoughts gun)
     
  2. joe0121

    joe0121 Well-Known Member

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    First thing that sticks out is what drag model are you using and what BC are you inputting. Though If you input info incorrectly the error would compound and I doubt you would remain dead on at varying ranges.
     

  3. backcountryguide

    backcountryguide Well-Known Member

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    I use the litz G7 BC that in the bullet library on the Shooter program. Ive double checked all my inputs and my 100 yard zero is a tiny bughole so I know Im not off there. Cant figure this out. Is it possible the barrel is that fast?
     
  4. westcliffe01

    westcliffe01 Well-Known Member

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    Did you read the owners manual thoroughly ? I have one on the way, so have not handled it yet and they have a section on calibrating the elevation to barometric pressure if you change elevation.

    From the 4500 manual:
    "Barometric Pressure and Altitude Adjustment
    The Kestrel Meter measures “station” pressure—the actual air pressure in the measurement location— and uses this value to calculate barometric pressure and altitude. Station pressure changes in response to two things—changes in altitude and changes in the atmosphere. Because the Kestrel Meter is constantly changing location and altitude, it is important to enter adjustments or “references” when accurate pressure and altitude readings are needed.

    Barometric pressure is station pressure corrected to sea level. In order to make the correction, the Kestrel Meter needs an accurate reference altitude. Altitude is the height above sea level. In order to correctly calculate altitude, the unit needs an accurate barometric pressure reference, also known as an “altimeter setting”. Fortunately, you only need to know ONE of these values (current barometric pressure or current altitude) in order to set your Kestrel Meter up to show accurate readings. "

    It then goes on to describe the procedure to make the adjustment.

    Altitude reduces drag, so if it thought your altitude/barometric pressure was wrong, it may increase the MV to compensate.

    Just check to be sure that part is calibrated properly. I didn't think this kind of calibration was needed but apparently it is.
     
  5. joe0121

    joe0121 Well-Known Member

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    Good Point. I have a yellow Kestral I got used off ebay a while back. It needs a new battery and also calibrated.
     
  6. rick523

    rick523 Well-Known Member

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    BCG this is a little off topic,but I am curious how do you input your dial up to get your velocity? I have shooter on iphone also but that is the one thing that always bugged me about it I can't get velocity validation that or I'm not smart enough to figure it out. Thanks for any info you can provide.
    Rick
     
  7. backcountryguide

    backcountryguide Well-Known Member

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    You have to set your reference Alt at 0 in the kestrel to get a corrected pressure mine is good to go. Theses tools have always worked for me with my other rifles. I guess what I am saying is this is not my first rodeo. I just cant see that speed from a Creedmoor. Your Iphone has velocity calibration within the shooter program and you can get to it from the drop table page. It brings up a separate menu were you put in your distance and the drop used to obtain hits and recalculates your muzzle velocity to match your drops.I have the kestrel 2500 nv
     
  8. westcliffe01

    westcliffe01 Well-Known Member

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    So you set your station altitude to sea level ? If the ballistic software thinks you are at a lower altitude then the drag will be higher and the only way to overcome it is for the velocity to be higher.

    Which model kestrel exactly do you have ? You might have been making the same mistake on every rodeo. It only matters if you care what it says the velocity is, if you want to correct that you might have to correct the elevation/pressure on your meter first.

    from 4500 manual
    "Starting with a known altitude for your location

    You can obtain your altitude from a topographical map or local landmark. Google Earth is an excellent free program that provides the exact altitude for any given address: Google Earth.
    Set this value as your reference altitude on the BARO screen to determine your barometric pressure:
    Press the "-" button to enter the reference setting mode. Press the ">" button to increase the reference altitude or "<" the button to decrease the reference altitude.

    You will notice that the barometric pressure will change with changes in the reference altitude. Press the "-" button to exit the adjustment mode. Again, allow the Kestrel Meter to stabilize, then enter the value from the BARO screen as your reference pressure on the ALTITUDE screen by following the same procedure. Both readings are now accurate."
     
  9. backcountryguide

    backcountryguide Well-Known Member

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    At the end of the manual for the Kestrel 2500 it says if you wish to know the actual or station pressure for your location simply set he reference altitude to 0. In this case the Kestrel meter will not make any adjustments and will display the measured value. Ballistics software refer to atmospheric or station pressure as absolute pressure. These applications are concerned with the actual air density as opposed to pressure gradients relating to weather, so barometric pressure is less useful. this is how my Kestrel is set up. The bullet only cares about the absolute pressure it travels through as I understand it. That is unless all my rodeos are screwed up like you said. Someone please correct me if I am wrong on this.
     
  10. westcliffe01

    westcliffe01 Well-Known Member

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    ABOUT BAROMETRIC PRESSURE AND ALTITUDE ADJUSTMENTS
    The Kestrel Meter measures “station” pressure, the actual air pressure in the measurement location, and uses this value to calculate barometric pressure and altitude. Station pressure changes in response to two things—changes in altitude and changes in the atmosphere.
    Because the Kestrel Meter is constantly changing location and altitude, it is important to enter adjustments or “references” when accurate pressure and altitude readings are needed.

    Barometric pressure is station pressure corrected to sea level. In order to make the correction, the Kestrel Meter needs an accurate reference altitude. Altitude is the height above sea level. In order to correctly calculate altitude, the unit needs an accurate barometric pressure reference, also known as an “altimeter setting”. Fortunately, you only need to know ONE of these values (current barometric pressure or current altitude) in order to set your Kestrel Meter up to show accurate readings.

    Starting with a known altitude for your location
    You can obtain your altitude from a topographical map or local landmark. Google Earth is an excellent free program that provides the exact altitude for any given address: Google Earth.
    Set this value as your reference altitude on the BARO screen to determine your barometric pressure: simultaneously press "< and >" buttons to adjust the reference altitude.
    Press "< or >" to adjust the reference altitude, or hold "< or >" to adjust the value quickly. You will notice that the barometric pressure will change with changes in the reference altitude.

    Simultaneously press "< and >" to exit the reference altitude adjustment. Again, allow the Kestrel Meter to stabilize, then enter the value from the BARO screen as your reference pressure on the ALTITUDE screen by following the same procedure. Both readings are now accurate."
     
  11. backcountryguide

    backcountryguide Well-Known Member

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    So I need to get my altitude ref set in my baro screen and I should be good to go?
     
  12. rinodods

    rinodods Well-Known Member

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    This is how I've always had mine setup. Don't care to have a corrected reading. You just need to make sure which type your software is expecting and know the difference.
     
  13. backcountryguide

    backcountryguide Well-Known Member

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    Just tried it the other way and that is way off in every way. The drops are correct but something is off because this is the input Shooter asks for when you use the pressure absolute option. Thanks all for the help
     
  14. rinodods

    rinodods Well-Known Member

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    crazy question but what direction were you shooting?