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  • wind math help

    $this->unconvert_size(12pt;line-height:100%">Hello,</span>

    <span style="font-size:12pt;line-height:100%"> </span>

    <span style="font-family:Times New Roman"> I need to know the math formula for making wind drift corrections from inches to MOA. Please explain it like I am a 5 year old kid.


    Thanks,
    Dsmith261)


  • #2
    Check for the wind direction using the ever present wind direction tool. Hold into the wind about much. Press the trigger and ask for assistance.


    So simple even a five year old cave man can do it!
    Dave Bahde

    Training is the key to survival, the harder you train, the more likely you are to survive!

    Comment


    • #3
      a wind direction tool is only good at the location you will be shooting from. Variations of wind speeds or direction based on terrain are common in some real world applications. This is true wether it's using a rifle, or bow.

      I usually keep two 3x5 index cards laminated with the current ammo information. One side of card A has a range chart and card B has my windage chart. Unfortunately my windage chart is all mathmatical based.

      shooting with a tail wind or head on should get a 0 value for drift

      with a wind directly from your 3 or 9 - full value for drift
      with a wind at 130/430/730/1030 count it as a 3/4 ( 75)% value

      most wind value estimations require alot of practice, to the point of it becoming automatic to estimate both windage and range w/o optics everywhere I go.

      Basic formula I use is 1moa == 1" @ 100yds which is not 100 % accurate. I would need to break out my old infantry mortar manuals to get the most accurate.

      iirc 1 moa is equal to 1 foot at 1000 yds, but my mortar and surveying books are locked up at my parents

      I also remember reading about a forumla that was good to 500m by marines.

      If you have a windage chart and can estimate wind/range fairly well, basic rule my grandfather taught me is 1" == 1moa @100yds, 2" == 2moa@200yds, ect. Helps with verifying your property line also.
      Never under estimate the mindset of an engineer; if it is broke... fix it, if its not broke then it can be broke beyond any manner of repair in violent chaotic ways ( unintentionally of course .. yeah right ).

      Comment


      • #4
        If you have access to a external balistics software program, you can print off a card with a one mile an hour wind drift for your load. Then use this formula: Estimated Wind Speed in MPH x One MPH Drift from card / Range. Example: (I pulled these numbers out of my head, so DON'T USE THEM) I estimate a 10 MPH wind and my drift card reads 8.7 for one MPH wind at 550 yards. Rangefinder reads 555 yds. 10 x 8.7= 87/5.55=15.68, which equals 15.75 MOA drift correction. Push 15.75 MOA into your wind and if your estimates are correct you'ld get a hit. It takes a while but with pratice it works well. A pre-made drift card would work much faster but you still need to learn to read the wind.
        Hope this helps,


        J.D. Larsen
        Semper Fi!!

        Comment


        • #5
          Very interesting Larsenj. I'm going to see if it works with metric measurements. It should.
          "Don't die wondering"

          Comment


          • #6
            Larsen, I think your constant of 8.7 is pretty low for most projectiles (I know you were just going by memory). The general formula I recall for a 9:00 or 3:00 crosswind in a .308/'06 was: D (distance/100) times V (wind velocity in MPH) divided by 15 (the constant out to 600 yards). Basically, if D: 555/100 (5.55) x V (10): 55.5 / 15 = 3.7MOA which is far more realistic for a 10MPH wind at 555 yards, which equates to roughly 21.5". This will get you on paper, but as with most ballistic issues, YMMV, and your ACTUAL shots on paper are the most critical. Winds angled to the shooter (half or quarter value winds) require relevant reductions. I've used it out to 1/4 mile on coyotes and it does OK.

            The easiest way to do this is to get a laminated ballistic card from a good Highpower shooting supply house. They have them pre-made in a variety of calibers and loads. FWIW, when I started shooting my 7mmRUM, there were no charts to go by. After getting some early numbers, I took a .308 Palma chart and divided the MOA by 5 at 1,000 yards. It got me on paper. My 'reduced' load these days with a set-back barrel gets a constant of 4. Works for me.

            Comment


            • #7
              [quote]
              Larsen, I think your constant of 8.7 is pretty low for most projectiles (I know you were just going by memory). The general formula I recall for a 9:00 or 3:00 crosswind in a .308/'06 was: D (distance/100) times V (wind velocity in MPH) divided by 15 (the constant out to 600 yards). Basically, if D: 555/100 (5.55) x V (10): 55.5 / 15 = 3.7MOA which is far more realistic for a 10MPH wind at 555 yards, which equates to roughly 21.5". This will get you on paper, but as with most ballistic issues, YMMV, and your ACTUAL shots on paper are the most critical. Winds angled to the shooter (half or quarter value winds) require relevant reductions. I've used it out to 1/4 mile on coyotes and it does OK.

              The easiest way to do this is to get a laminated ballistic card from a good Highpower shooting supply house. They have them pre-made in a variety of calibers and loads. FWIW, when I started shooting my 7mmRUM, there were no charts to go by. After getting some early numbers, I took a .308 Palma chart and divided the MOA by 5 at 1,000 yards. It got me on paper. My 'reduced' load these days with a set-back barrel gets a constant of 4. Works for me.[/b]
              Your right but I don't think you're following me. I was pulling those numbers out of my "six" for math purposes only. Using my ballistics software I got a
              -2.47 drift in a 1MPH wind at 550 yds. Using my formula in a 10MPH wind would go as follows: 10x2.47=24.7/5.50=4.49MOA. Granted it's a bit much but it would produce a hit on a man sized target. I looked in my personal wind chart and I got 3.50MOA for my rifle. What happens to your constant at 600+ yds? Your formula does seem to be more accurate. I like it!
              Take care,


              J.D. Larsen
              Semper Fi!!

              Comment


              • #8
                Thank you very much for the info. I have the long range shooting simulation i have be practicing on before i attempt to go out on the range. I still have some problems with range but i'm getting better. Thanks againe.

                Dsmith261

                Comment


                • #9
                  Larsenj brings up a good point speedbump. What happens after 600yrds? Can you explain?

                  John 3:16
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                  Romans 12:1-2
                  Therefore, I urge you, brothers, in view of God's mercy, to offer your bodies as living sacrifices, holy and pleasing to God--this is your spiritual act of worship. [2] Do not conform any longer to the pattern of this world, but be transformed by the renewing of your mind. Then you will be able to test and approve what God's will is--his good, pleasing and perfect will.

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                  • #10
                    Gotcha Larsen , thought that might be it, and I'm glad I'm not the only one cerebrally challenged around here.

                    As far as the constant, it'll decrease as the distance goes past 600. I think it's 10 at 1K, but I'm not sure. That'll require more MOA adjustment the farther out you go. I don't recall the exact #s, it's been 15 years since I used something other than a data card, and I've gotten rusty!

                    Comment


                    • #11
                      [quote]
                      Gotcha Larsen , thought that might be it, and I'm glad I'm not the only one cerebrally challenged around here.

                      As far as the constant, it'll decrease as the distance goes past 600. I think it's 10 at 1K, but I'm not sure. That'll require more MOA adjustment the farther out you go. I don't recall the exact #s, it's been 15 years since I used something other than a data card, and I've gotten rusty![/b]
                      LOL! I hear ya. Check and see if you can locate those numbers for 700, 800, and 900 yds. If you can't, I can probably play with the numbers until it works. I also use a wind card most of the time but it's nice to have a back up just in case.
                      Thanks again,


                      J.D. Larsen
                      Semper Fi!!

                      Comment


                      • #12
                        [quote]
                        <div class='quotemain'>Gotcha Larsen , thought that might be it, and I'm glad I'm not the only one cerebrally challenged around here.

                        As far as the constant, it'll decrease as the distance goes past 600. I think it's 10 at 1K, but I'm not sure. That'll require more MOA adjustment the farther out you go. I don't recall the exact #s, it's been 15 years since I used something other than a data card, and I've gotten rusty![/b]
                        LOL! I hear ya. Check and see if you can locate those numbers for 700, 800, and 900 yds. If you can't, I can probably play with the numbers until it works. I also use a wind card most of the time but it's nice to have a back up just in case.
                        Thanks again,
                        [/b]

                        WOOOHOOO Found it! First Edition of The Ultimate Sniper page 294

                        Based on the formula used for the 1903-A3 Springfield

                        (Range in 100yds X Speed in MPH ) / (constant ) = MOA windage

                        Constants
                        upto 500 yds = 15
                        600yds = 14
                        700 yds = 13
                        800 yds = 13
                        900 yds = 12
                        1000 yds = 11
                        Never under estimate the mindset of an engineer; if it is broke... fix it, if its not broke then it can be broke beyond any manner of repair in violent chaotic ways ( unintentionally of course .. yeah right ).

                        Comment


                        • #13
                          [quote]
                          WOOOHOOO Found it! First Edition of The Ultimate Sniper page 294

                          Based on the formula used for the 1903-A3 Springfield

                          (Range in 100yds X Speed in MPH ) / (constant ) = MOA windage

                          Constants
                          upto 500 yds = 15
                          600yds = 14
                          700 yds = 13
                          800 yds = 13
                          900 yds = 12
                          1000 yds = 11[/b]
                          You da Man!! You saved me form having to tick away at the calculator for a while. Thanks! I'll check it against my wind drift cards.
                          Thanks Again,


                          J.D. Larsen
                          Semper Fi!!

                          Comment


                          • #14
                            Guys if your break down the 10 mph numbers in inches ( add dismal point between the numbers). The standard formula is inches X wind speed, divided by 1 moa of the distance.

                            Example:

                            600 yards= 3.0" inches
                            wind speed= 8 mph

                            3" X 8mph=24"
                            Now you need to convert this into moa so you can dial it in your scope. Simply divide this by 1 moa of your distance.

                            24"/ 6= 4.0 moa.

                            Now this is always figured as a full wind first. Then if the wind is say from 1:30 multiply .707 which is 70% of a full wind, times you wind reading. (4.0 moa) = 2.8 moa rounded to the nearest 1/4 moa. 2.75 moa
                            If the wind is coming from 2 o'clock multiply this by .866 which is 86% of a full wind.

                            If it's coming from 1 o'clock use .5 or 1/2 of the total moa reading.

                            Be sure to read the wind at your muzzle, then half way to the target and finally at the target. Average the three winds to get you speed.

                            Wind drift is over 100 years old and is an exact formula.


                            Take care, flea
                            "with the patience of an oyster....I watch and wait"

                            Training the US, one shooter at a time.






                            http://www.centralvirginiatactical.com

                            Comment


                            • #15
                              [quote]
                              Guys is you break down the 10 mph numbers in inches ( add dismal point between the numbers). The standard formula is inches X wind speed, divided by 1 moa of the distance.

                              Example:

                              600 yards= 3.0" inches
                              wind speed= 8 mph

                              3" X 8mph=24"
                              Now you need to convert this into moa so you can dial it in your scope. Simply divide this by 1 moa of your distance.

                              24"/ 6= 4.0 moa.

                              Now this is always figured as a full wind first. Then if the wind is say from 1:30 multiply .707 which is 70% of a full wind, times you wind reading. (4.0 moa) = 2.8 moa rounded to the nearest 1/4 moa. 2.75 moa
                              If the wind is coming from 2 o'clock multiply this by .866 which is 86% of a full wind.

                              If it's coming from 1 o'clock use .5 or 1/2 of the total moa reading.

                              Be sure to read the wind at your muzzle, then half way to the target and finally at the target. Average the three winds to get you speed.

                              Wind drift is over 100 years old and is an exact formula.


                              Take care, flea[/b]
                              Holy Crap! "Oh no I've gone cross-eyed!" Where did the 600 yds = 3.0" come from? Is there an easier way to get the same result? I mean, I'd spend ten minutes doing math problems before I could take a shot doing it like that. Do you actually do all that or does it become natural with experience?
                              Thanks Vern,


                              J.D. Larsen
                              Semper Fi!!

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