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Plotting a Graph from Known Drop Points?

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  #1  
Unread 11-18-2003, 07:17 PM
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Location: Fairmont, WV
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Plotting a Graph from Known Drop Points?

O.K., I'm a little new to this, so any help would be appreciated. This is my first post, but I've been lurking around for a while. I've tried a few of the "freeware" ballistic programs and an Excel spreadsheat that I found on another site in addition to the trial version of RSI's Ballistics program, but none of these seem to calculate the correct curve for my particular rifle and load. I'm shooting a 7mm RUM with 26" Douglas barrel. 139 grain Hornady SST's on 93.5 grains of Reloader 25. at 3465 FPS 15 feet from muzzle. One of the programs I'm using corrects this velocity to 3476 at the muzzle, so I've been using that number as muzzle velocity. I'm at about 975 feet above sea level and it's been about 50 degrees here. From shooting at various distances, I've determined that I'm +2.5in.@100Yds, +1.75in.@250, -10in.@400, and -14in.@450. The rifle also has a 20MOA one piece incline base on it, and I'm not sure if this is a factor. Heigth of the scope at the front bell is 1.828 center of bore to center of tube. Now for the question. Is there any way to take these 4 points and plot a graph where I can see drop every 10 feet from 100 Yds to 1000. Sorry this was so long, but thanks in advance for your help.
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  •   #2  
    Unread 11-18-2003, 07:51 PM
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    Re: Plotting a Graph from Known Drop Points?

    If you are going to hunt with the rifle you will probably not need a drop-chart in 10 foot or even ten yard increments. Maybe the 1000 yard shooters would use one that fine but we have determined that 25 yard increments work great. We shoot our drops on paper. Did that before deer season all the way out to 650 which is as far as we would shoot with our rigs.
    There are no doubt computer programs which will do what you need, check EXBAL as it seems to be very popular with guys here. Do a search for Perry Systems and EXBAL and you will find their site.
    Good luck with your shooting.
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      #3  
    Unread 11-18-2003, 07:59 PM
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    Re: Plotting a Graph from Known Drop Points?

    Sorry, typed that wrong, meant 10 YDS, but i'm sure 25 would be more than enough. Trouble is, I don't have enough flat land where I live to shoot at all the distances that are available where I'm planning on hunting. Don't think I'll take any shots past the 450yds I shot at today, but need some idea of where I'm at between 250 and 400yds. Guess I'll keep adjusting BC's 'till i get something to resemble my known drops.
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      #4  
    Unread 11-18-2003, 09:08 PM
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    Re: Plotting a Graph from Known Drop Points?

    Hello Stugotz,

    I played around with a program for a while, adjusting the velocity only. Velocity can often be the guesswork after all. I was able to duplicate your path quite well with the MV being 3450 and zeroed at 290 yds, everything else being equal.

    I would trust the BC -based trajectory with the shooting you have done rather than tweak the BC.

    Close enough to get an idea,I hope.


    0 3450 3675 0,000 -1,82
    25 3389 3546 0,021 -0,54
    50 3330 3423 0,044 0,55
    75 3272 3305 0,066 1,45
    100 3214 3189 0,09 2,15
    125 3158 3079 0,113 2,63
    150 3103 2973 0,137 2,90
    175 3049 2870 0,161 2,94
    200 2995 2769 0,186 2,75
    225 2943 2674 0,212 2,32
    250 2892 2582 0,237 1,63
    275 2841 2492 0,263 0,69
    300 2791 2405 0,29 -0,52
    325 2743 2323 0,317 -2,01
    350 2695 2242 0,345 -3,79
    375 2647 2163 0,373 -5,87
    400 2601 2089 0,401 -8,26
    425 2556 2017 0,43 -10,97
    450 2511 1947 0,46 -14,01
    475 2467 1879 0,49 -17,39
    500 2424 1814 0,521 -21,14
    525 2382 1752 0,552 -25,24
    550 2340 1690 0,584 -29,74
    575 2299 1632 0,616 -34,63
    600 2259 1575 0,649 -39,93

    Man,I hope this shows properly.
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      #5  
    Unread 11-18-2003, 09:14 PM
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    Re: Plotting a Graph from Known Drop Points?

    It does! [img]images/icons/grin.gif[/img]

    Left to right: Distance,Velocity,Energy,Time Of Flight,Drop.

    I left wind drift etc. out so it is readable.

    EDIT: Yes,this is the 7mm Hornady 139 grain SST ,BC .486. Better shoot some more groups in those 250 to 400 distances before hunting, this can be all wrong after all.

    Itīs the only sure way. Good luck,hope this helps.

    [ 11-18-2003: Message edited by: Petander ]
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      #6  
    Unread 11-20-2003, 10:21 AM
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    Re: Plotting a Graph from Known Drop Points?

    Thanks Petander!!! What program did you use to get these results? Do you know which drag function it uses (G1,G5,G7)?
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      #7  
    Unread 11-20-2003, 01:51 PM
    700 700 is offline
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    Re: Plotting a Graph from Known Drop Points?

    Stugotz

    I do not douth your MV of 3476fps or your value of 2.5 inches high at 100 yards. 100 Yards is quite close to your shooting position and so the effect of errors is limited.

    Taking these values and a G1 BC of 0.486 I got the following drop table:-

    Range Yrds,Range Mts,Velocity Ft.S-1,Energy Ft.Lb,Momentum Lb.S,Drop In,Drop CM
    0,0,3476.03,3729.09,2.1456,-1.828,-4.64312
    25,22.86,3421.16,3612.29,2.11173,-0.462704,-1.17527
    50,45.72,3366.97,3498.77,2.07829,0.716986,1.82114
    75,68.58,3313.45,3388.41,2.04525,1.70505,4.33082
    100,91.44,3260.56,3281.11,2.0126,2.49524,6.33791
    125,114.3,3208.31,3176.78,1.98035,3.08109,7.82598
    150,137.16,3156.66,3075.33,1.94847,3.45589,8.77797
    175,160.02,3105.61,2976.67,1.91696,3.61268,9.17621
    200,182.88,3055.15,2880.72,1.88581,3.54423,9.00234
    225,205.74,3005.25,2787.39,1.85501,3.24303,8.23729
    250,228.6,2955.92,2696.63,1.82456,2.7013,6.86129
    275,251.46,2907.14,2608.35,1.79445,1.91093,4.85376
    300,274.32,2858.89,2522.5,1.76467,0.863516,2.19333
    325,297.18,2811.18,2439.01,1.73522,-0.449695,-1.14223
    350,320.04,2763.99,2357.81,1.70609,-2.0378,-5.17602
    375,342.9,2717.32,2278.86,1.67728,-3.91027,-9.9321
    400,365.76,2671.16,2202.09,1.64879,-6.07696,-15.4355
    425,388.62,2625.5,2127.46,1.62061,-8.54813,-21.7122
    450,411.48,2580.35,2054.91,1.59274,-11.3344,-28.7895
    475,434.34,2535.68,1984.38,1.56517,-14.4471,-36.6955
    500,457.2,2491.51,1915.85,1.5379,-17.8975,-45.4598
    525,480.06,2447.82,1849.25,1.51094,-21.698,-55.1129
    550,502.92,2404.62,1784.55,1.48427,-25.861,-65.687
    575,525.78,2361.9,1721.7,1.4579,-30.3998,-77.2155
    600,548.64,2319.65,1660.66,1.43182,-35.328,-89.7332
    625,571.5,2277.88,1601.38,1.40603,-40.66,-103.276
    650,594.36,2236.58,1543.84,1.38054,-46.4107,-117.883
    675,617.22,2195.62,1487.81,1.35526,-52.5957,-133.593
    700,640.08,2154.93,1433.19,1.33015,-59.2314,-150.448
    725,662.94,2114.64,1380.09,1.30527,-66.3349,-168.491
    750,685.8,2074.75,1328.52,1.28065,-73.9243,-187.768
    775,708.66,2035.29,1278.46,1.2563,-82.0185,-208.327
    800,731.52,1996.27,1229.92,1.23221,-90.6372,-230.218
    825,754.38,1957.72,1182.87,1.20841,-99.8011,-253.495
    850,777.24,1919.63,1137.29,1.18491,-109.532,-278.211
    875,800.1,1882.04,1093.18,1.1617,-119.852,-304.425
    900,822.96,1844.94,1050.51,1.1388,-130.786,-332.197
    925,845.82,1808.35,1009.25,1.11622,-142.359,-361.591
    950,868.68,1772.28,969.39,1.09395,-154.595,-392.672
    975,891.54,1736.73,930.892,1.07201,-167.524,-425.511
    1000,914.4,1701.71,893.731,1.05039,-181.173,-460.18

    With values corrected for your altitude and temperature.

    These values were confirmed by two seperate programs which only showed a difference of 1 inch at 1000 yards.

    At ranges other than 100 yards, my drops are out of whack with yours. At 400 yards you get a drop of 10 inches and my tables show 6 inches.

    Perhaps some thing you could check for is canting. This may be due to the scope not being aligned properly on the vertical/horizontle axis or maybe you are holding the rifle at a slight angle. Canting will cause point of impact error which increase exponentially at longer ranges.

    Another thing to check is are the given distances correct. My tables give 6 inches drop at 400 and 10 inches drop at 450 yards. 10 inches is the drop you give at 400 yards. Perhaps your range measurments might be off.

    If you email me at brian_sinnott@hotmail.com I will send you a chart showing the drops given above.

    Rgds

    700

    [ 11-20-2003: Message edited by: 700 ]
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