Verifying BC

Discussion in 'ELR, Ballistics & Bullets Board' started by Toby Bradshaw, Jul 31, 2017.

  1. brians356

    brians356 Gold $$ Contributor

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    Thanks, it's almost becoming Everclear now. Or time for some, anyway.

    He also mentioned Doppler radar. How commonly is that used in the F-class community?
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    Last edited: Aug 22, 2017
  2. ballisticdaddy

    ballisticdaddy Silver $$ Contributor

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    Actually since the Labradar has become popular you see them at most F-class matches as they do not change the POI as the MagnetoSpeed. Doppler is being utilized by Hornady for tracking projectiles......http://bulletin.accurateshooter.com...cs-calculator-uses-doppler-radar-bullet-data/
     
  3. gstaylorg

    gstaylorg Silver $$ Contributor

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    FWIW - it is currently not legal to use a chronograph during an F-Class match. However, as noted by ballisticdaddy, the Labradar has become a popular chronograph for F-Class shooters.
     
  4. IdahoSharpshooter

    IdahoSharpshooter Gold $$ Contributor

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    I am reasonably happy with my M43 out to 600 yards.

    I need to spend more time behind the rifle butt, as opposed to in front of the computer.
     
  5. SheepDog

    SheepDog Silver $$ Contributor

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    The LabRadar is the only retail Doppler radar chronograph on the market as far as I know and the OP is talking, if I am not mistaken, about using a commercial doppler radar. In order to track a bullet for ten seconds you need both a high frequency and a high powered radar. The bullet would have to be fired at quite an angle too. Wind isn't the only variable over that distance, the air density can also change with humidity and pressure when it covers 10 seconds of flight.
     
  6. SheepDog

    SheepDog Silver $$ Contributor

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    Hornady says the 4DOF software is the most accurate and that there are no others that are more accurate. There are 2 commercially available programs that use 6 degrees of freedom that are more accurate than the Hornady program. The price for these two programs is about the same as you pay for a rifle needed to necessitate their use. ($1700 to $2200 each)
    I am currently working on a 6DOF ballistics calculator written in C for the open source software community. It won't have a pretty user interface but it will produce a table of projected ballistics as long as the user puts in the data (a minimum of 18 pieces of information just to use in the calculations). When I get it done it will be completely portable to any operating system with a C compiler. Open source software is free to use and free to redistribute. There is no money being made on the sale or distribution with the exception of paying for the CD it is recorded on and the reasonable cost of duplication. It will be available for free to download the source code and under the open source copyright it can be modified as long as the modifications are listed and full credit is given to all participating authors. So I would expect that it would be improved with a nice GUI and maybe tables of bullets with the information necessary to help with some of the input.
     
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  7. Berger.Fan222

    Berger.Fan222

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    NRA added this to the high power rules in 2017, but as far as I know most non-NRA F-Class matches (club matches) still allow use of the LabRadar during matches. Also, note that the NRA rule reads:

    (b) Radars, chronographs and other devices designed to measure bullet velocity are prohibited on the line.

    If provision is made for an external trigger, the LabRadar can actually be used from behind the firing line, which would not violate this rule.
     
  8. Berger.Fan222

    Berger.Fan222

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    Most bullets don't make it past 5000 yards in 10 seconds. For example, the 200.20x at a muzzle velocity of 2700 fps makes it to close to 3500 yards under standard conditions. Depending on the maximum allowed wind, it is possible to know that the wind is below a specified maximum for distances of that order. One might be limited to testing on calm mornings.
     
  9. Berger.Fan222

    Berger.Fan222

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    It'll be nice to have, but those aerodymanic coefficients needed for accurate 6DOF modelling are not available for most bullets.
     
  10. T-shooter

    T-shooter

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    Interesting. When do you plan to have it finished?
     
  11. SheepDog

    SheepDog Silver $$ Contributor

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    There is no plan on WHEN. I work on it when I get time. Right now I am working on calculating the angle of departure for a zero at a given range. Once I do that then I have to build a recursive algorithm for the output. Then, a bit of testing, and the beta testing followed by the first release. A working model will get others interested in improvements and translations to other languages. This will be the third ballistics program I have written but the other two were only 3 DOF.
     
  12. VaRandy

    VaRandy Silver $$ Contributor

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    Very interested in following your progress. I am working regularly out to 1500 or so and have paid a lot of attention to BC. My dream would be to know the average BC of a bullet from muzzle to target distance for any chosen distance.
     
  13. Ballisticboy

    Ballisticboy

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    I will try to answer as many points as I can, though as I am sure you will understand, I have to be careful what I say. On the question of % for match bullets I have only tested one or two of those. The Cd variability changes depending on the Mach number. We are not producing a single Cd value but a complete Cd/Mach number curve for each bullet. The Cd variability of a good design is around a few %, some of them are incredibly consistent. Their consistency also gives confidence in the experimental method. Supersonic bullets at supersonic speeds demonstrate good consistency, again a few % but probably a couple of % worse than the best designs so say +/-3-4%. Subsonic MV bullets tend to be the worst, with variabilities typically 7-8%.
    My background is in aeroballistics of all gun launched projectiles from large calibre weapons (up to 1 metre in diameter) down to particle size objects. Been doing it for nearly 40 years now. Everything I have reported here is for small calibre bullets, 0.5 inch or less. All we are doing is applying large calibre testing practices to bullets. The muzzle velocity radars are like Labradar with fixed heads but much more powerful and expensive. The tracking radar is not fixed head. It is very powerful and would not do you much good if you were in front of it. That is why the guns have to be stand mounted.
    When you say the bullets will travel 7000 to 10000 yards in 10 seconds I take it you mean feet. The only projectiles I know of which can go 10000 yards in 10 seconds are tank rounds. The 0.5 inch bullet travels the furthest I know of in 10 seconds, about 3500 metres. It is also the least effected by wind. We fire out to sea and every method imaginable is used to monitor the atmosphere with strict limits on maximum wind speeds. Of the data we collect only the first 2-3 seconds gives good quality data which can be used for the extensive analysis carried out. The radar does track the bullets more or less to splash but the data is not so good.
    The air density changes are minimal over the distances and heights we use for the trials.
    At the moment only Cd is being computed but the radar data could be used to produce full six degree of freedom input data. That is the biggest problem with bullet aerodynamic data, it simply does not exist in most cases though there are some free aerodynamic prediction programs around which can give a starting point.
     
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  14. JPeelen

    JPeelen

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    Thank you very much for your response and for your patience explaining.

    A historical note: Aberdeen Proving Ground started by using a modified (Hawk AA missile) target illuminating radar, which had a power of 125 Watts. First measurements of small arms bullets were done in October 1965.
     
  15. brians356

    brians356 Gold $$ Contributor

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    How will we know when compilable C code is available?
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  16. wwbrown

    wwbrown Silver $$ Contributor

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    One problem with the measurements of BC that Courtney et al. did in the paper referenced was the BC was measured over the first 200 yards of the trajectory. Making measurements of the last 200 yards from 800 to 1,000 yards of the trajectory would provide better data as the bullet is dropping faster in that region than the first 200 yards.
     
  17. T-shooter

    T-shooter

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    Just a thought, could you calculate the angle (with zero scope height) as a simple right triangle using the true target distance as one side and the bullet drop at that distance as the other?
     
  18. SheepDog

    SheepDog Silver $$ Contributor

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    Brians356,
    If you like I will post the availability here as well as other places letting you know where the program and code is available.

    T-shooter,
    I could do that but the height of the sight is tied to the angle so it has to be input from the beginning. I have to have the program compute the actual drop with all the data points and then from that derive the MOA and then convert it to degrees at the muzzle. The concept is easier to deal with than the code. It has to be computed for each set of data due to atmospheric, and gravitational changes as well as zero distance. The process is one of calculating the angle using the ballistics from a level gun zero'd at the users range and the recalculating it using the angle over the same distance in increments of one yard and printing it on the screen in the increments set by the user. There are 228 lines of code just getting ready to begin the calculations not counting the code referenced in the 45 different structures that are used to calculate each step. (a structure is a sub program inside the program)
     
  19. Berger.Fan222

    Berger.Fan222

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    I love the idea of a 6DOF program, but I wouldn't bother with an iterative approach to finding the launch angle for a specified point of impact (zero range). The 3DOF and 4DOF (point mass and modified point mass) can do that because they are less computationally intensive and can numerically integrate the differential equations as many times as needed taking a "guess and check" approach (with Newton's method) to finding the launch angle needed for a specified zero.

    I'd be happy enough with a reliable 6DOF code that could compute the trajectory for a given elevation (angle of bore relative to scope line of sight). Knowledgable users can always use their favorite 3DOF or 4DOF calculator to determine good guesses for the desired elevation and then do the guess and check bit manually from there, if desired. Most computers are gonna be too slow to integrate the 6DOF equations as many times as most codes integrate the 3DOF equations to determine the elevation angle.

    It's not just that you have 6 degrees of freedom, your time steps will need to be much smaller to account for the nutation and precession motions. 1000 time steps might be plenty for an accurate 3DOF calculation, but in a 6DOF, you need 100-1000 steps for whatever the highest frequency coning motion is.
     
  20. Berger.Fan222

    Berger.Fan222

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    Not so. The table below shows that Doppler radar can only provide four of the many aerodynamic coefficients. The ARL Spark Range (or equivalent) is needed to get them all.

    (Table from p. 21 of https://ndiastorage.blob.core.usgovcloudapi.net/ndia/2012/armaments/Wednesday13615siewert.pdf )

    Figuring out how to get more of the coefficients without using the spark range is an active field of research right now.

    See:
    https://ndiastorage.blob.core.usgovcloudapi.net/ndia/2012/armaments/Wednesday13615siewert.pdf

    https://ndiastorage.blob.core.usgovcloudapi.net/ndia/2011/gunmissile/Tuesday11774_Dohrn.pdf

    https://ndiastorage.blob.core.usgovcloudapi.net/ndia/2005/22ndISB/tuesday/dupuis.pdf

    https://ndiastorage.blob.core.usgovcloudapi.net/ndia/2006/smallarms/weinacht.pdf

    Aerodynamic Coefficients.JPG
     

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