Wind drift phenomenon

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Wind drift phenomenon

    I'm making a wind chart for my .264LBC to put in a field shooting guide for the rifle, and I'm experiencing something pretty wierd. I'm using JBM for wind drift values out to 1000 yards, using the 123 Scenar at 2560 from 10 ft from the muzzle, 40 degrees, 200 ft elevation, and 70% humidity. The wind drift MOA exactly matches the wind speed at 1000 yards all the way to 19 mph so far. I messed with different inputs to make sure it wasn't a fluke or an error, but it seems legit. Makes it pretty easy to remember your scope dope at 1000 if it holds true in real world shooting. Am I missing something (besides spin drift which I will account for).

  • #2
    I just ran your velocity using the defaults for temperature, elevation, and humidity and got to within 0.5 MOA of the 19 you mentioned. Changing the MV to 2350 ft/sec naturally increased the drift -- to a tad over 21 MOA.

    It looks like you may indeed have a lucky coincidence for the 1000 yard condition. What you could do is vary the MV up and down by 25 ft/sec, the elevation by a few thousand feet, the humidity from 35% to 95%, and the range from 990 to 1010 yards if the only range you're interested in is 1000. If the drift MOA stays within 0.5 of the wind speed in MOA for these variations, your chart becomes a LOT simpler!

    Comment

    • RangerRick

      #3
      "A Mile a Minute" has been a wind drift rule of thumb for a long time, i.e. one MOA for each mph of wind.

      RR

      Comment


      • #4
        Just starting this long range thing (past 600) so it was news to me. Hadn't seen it come out exactly like that on any of my other cartridges. 1/2 minute per MPH at 600 seems to hold true also.

        Comment

        • LR1955
          Super Moderator
          • Mar 2011
          • 3355

          #5
          Originally posted by blackfoot View Post
          I'm making a wind chart for my .264LBC to put in a field shooting guide for the rifle, and I'm experiencing something pretty wierd. I'm using JBM for wind drift values out to 1000 yards, using the 123 Scenar at 2560 from 10 ft from the muzzle, 40 degrees, 200 ft elevation, and 70% humidity. The wind drift MOA exactly matches the wind speed at 1000 yards all the way to 19 mph so far. I messed with different inputs to make sure it wasn't a fluke or an error, but it seems legit. Makes it pretty easy to remember your scope dope at 1000 if it holds true in real world shooting. Am I missing something (besides spin drift which I will account for).
          BF:

          Not having looked at it on a ballistics program, I bet that the figures come up to about 1/3 MOA / MPH Full value to 300; 1/2 MOA / MPH Full Value from 300 - 600; 3/4 MOA / MPH Full Value from about 600 - 900; and 1 MOA / MPH Full Value from 900 - 1100. More than adequate for targets that are reasonably sized for the low velocity of a 30 grain powder capacity cartridge.

          Another one you can use with that particular BC and basic velocity is a favor to 300, 1/2 MOA from 300 - 700, and 1 MOA from 700 - 1100.

          It depends on how simplified you want to go or how fast the wind is changing.

          They won't be perfect but neither is anyone's ability to get real wind data at every point to 1000 and then turn it into a solution.

          LR1955

          Comment

          Working...
          X