Longer range data and integrating it into rifle dope versus calculated trajectories..

JasonMPDJasonMPD Senior MemberPosts: 6,063 Senior Member
So getting out to 600 yards in a regimented environment allowed be to collect some good data for my Ruger Gunsite Scout rifle load-- 168gr Hornady HPBT Match and 44.6gr RL15. The Magnetospeed indicated an average of 2515 MV and a SD of 9.

With a 100 yard zero, I collected the following info...

200 yard drop was 4.3" (0.6 MRAD) - in doing trajectory validations, that meant my muzzle velocity was about 2480-2485 and not 2515 like the Magnetospeed indicated.

600 yard drop was 114" (5.3 MRAD) - I decided this was correct as bullet impacts were +/- 5" above or below the X-ring consistently. This further validated my observed dope at 200 yards for a 2480-2485 MV.

Is an error of 35 fps potentially nominal or reasonable for the Magnetospeed? It seems a bit...bad.
“There are three kinds of men. The one that learns by reading. The few who learn by observation. The rest of them have to pee on the electric fence for themselves.” – Will Rogers

Replies

  • Farm Boy DeuceFarm Boy Deuce Senior Member Posts: 5,996 Senior Member
    Being off by 35fps may be bad I don't know about that. You also aren't going to make your official dope card from calculated data.

    Your data for the initial dope was fairly close. As long as the Magneto speed gives consistent readings I would not worry about that too much. It seems accurate enough for load development.
    I am afraid we forget sometime that the basic and simple things brings us the most pleasure.
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  • PegasusPegasus Senior Member Posts: 2,472 Senior Member
    There are several data points used in calculating trajectories; the two most important ones are muzzle velocity and BC value. Some of the others are density altitude, humidity and so on. If these values are not exact in you calculations you will have deviations from reality.

    Before blaming the Magnetospeed, and thinking that the recorded MV is wrong, I would check all the other variables, especially the BC value used in the calculations.
  • JasonMPDJasonMPD Senior Member Posts: 6,063 Senior Member
    Pegasus wrote: »
    There are several data points used in calculating trajectories; the two most important ones are muzzle velocity and BC value. Some of the others are density altitude, humidity and so on. If these values are not exact in you calculations you will have deviations from reality.

    Before blaming the Magnetospeed, and thinking that the recorded MV is wrong, I would check all the other variables, especially the BC value used in the calculations.

    Ok.

    Other than published BC values (G1 of .453 for the Hornadays HPBT if I recall correctly), what other methods of BC calculation can be accomplished relatively simply?

    ETA: this time of year on the Florida coast the temp/hum/mmMg are pretty constant.
    “There are three kinds of men. The one that learns by reading. The few who learn by observation. The rest of them have to pee on the electric fence for themselves.” – Will Rogers
  • PegasusPegasus Senior Member Posts: 2,472 Senior Member
    My favorite calculator is on the Internet at jbmballistics.com. There are several calculators there, I use the one for trajectory and drift.

    There is a veritable plethora of parameters to set and the environmental ones are really what you are looking for here. Set the elevation (incorrectly identified as altitude at JBM,) the temperature and humidity and the current air pressure. Select the proper bullet from the list and if it says (Litz) as an option, use that one. This means the calculator will be using the data for that bullet as calculated by Bryan Litz, the current ballistics guru and all around good guy. You're in luck since there is an entry for your bullet corrected by Bryan. The G7 BC is .222.

    Enter your MV and distance from the muzzle (0), the zero range and once you have all that set, press the calculate button and voila.

    I would sooner trust the MV than any published BC value, but with Litz's BC values, it gets really close.
  • Ernie BishopErnie Bishop Senior Member Posts: 6,721 Senior Member
    Check out Litz's BC's - They are the ones I trust the most.
    Second, is your 100 yard zero truly spot on?
    Ernie

    "The Un-Tactical"
  • BigDanSBigDanS Senior Member Posts: 6,663 Senior Member
    I would recommend checking your altitude, temperature and humidity settings. Although warm in Florida, it is low elevation and humid, contributing to "thick air" which might slow a bullet faster, especially over distance.

    D
    "A patriot is mocked, scorned and hated; yet when his cause succeeds, all men will join him, for then it costs nothing to be a patriot." Mark Twain
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  • JasonMPDJasonMPD Senior Member Posts: 6,063 Senior Member
    Check out Litz's BC's - They are the ones I trust the most.
    Second, is your 100 yard zero truly spot on?

    Yes, very spot on. Like, eating up 1" dots at 100 yards.
    “There are three kinds of men. The one that learns by reading. The few who learn by observation. The rest of them have to pee on the electric fence for themselves.” – Will Rogers
  • JasonMPDJasonMPD Senior Member Posts: 6,063 Senior Member
    BigDanS wrote: »
    I would recommend checking your altitude, temperature and humidity settings. Although warm in Florida, it is low elevation and humid, contributing to "thick air" which might slow a bullet faster, especially over distance.

    D

    Temp was 90F, pressure 29.9 per the local data and humidity was 75%. That's a pretty good standard too for this area this time of year.
    “There are three kinds of men. The one that learns by reading. The few who learn by observation. The rest of them have to pee on the electric fence for themselves.” – Will Rogers
  • PegasusPegasus Senior Member Posts: 2,472 Senior Member
    BigDanS wrote: »
    I would recommend checking your altitude, temperature and humidity settings. Although warm in Florida, it is low elevation and humid, contributing to "thick air" which might slow a bullet faster, especially over distance.

    D


    Boy is that last comment wrong.

    High humidity makes the air thinner, thus reducing the drag on the bullet. It is well known that hot and humid makes bullets go faster whereas cold and dry slows them down.

    If water vapor was heavier than air, you would be rudely woken up during the night by clouds crashing to earth.

    ETA: Next we're going to be told that the speed of sound is a function of altitude or air pressure. I mean, really....
  • JasonMPDJasonMPD Senior Member Posts: 6,063 Senior Member
    Pegasus wrote: »
    Boy is that last comment wrong.

    High humidity makes the air thinner, thus reducing the drag on the bullet. It is well known that hot and humid makes bullets go faster whereas cold and dry slows them down.

    If water vapor was heavier than air, you would be rudely woken up during the night by clouds crashing to earth.

    ETA: Next we're going to be told that the speed of sound is a function of altitude or air pressure. I mean, really....

    +1

    Benchrest guys like to shoot in a slight drizzle. Thinner air, still air.

    And to the cloud comment...

    Clouds stay up, rain comes down. Gaseous versus liquid. Super humid air feels "thick" because it's has less oxygen density for your lungs to enjoy. And feels muggy because sweat doesn't evaporate quuckly. That's that.
    “There are three kinds of men. The one that learns by reading. The few who learn by observation. The rest of them have to pee on the electric fence for themselves.” – Will Rogers
  • HvyMaxHvyMax Senior Member Posts: 1,786 Senior Member
    Once you enter a few corrections into the programs they usually tighten up to near perfect.
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    Reason for editing: correcting my auto correct
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